I've finally completed my run. First, brief summaries of the remaining fights:
Iris: started with Stouland fighting for the sake of interest, got Dragon Tailed eventually and Escavalier tanked its way through the remainder
Marshall: Swoobat wasn't able to handle throw so ran it again with Serperior in the lead and although it was a long fight Serprior eventually was able to sweep through
Grimsley: Stoutland can play vs Scrafty of all things, Brick Break doesn't 2HKO after Intimidate. The Serprior show again, Coil+Seed set up on Krookodile, only Bisharp as a stumbling block but it goes down eventually
Caitlin: The Escavalier show, tanking a Focus Blast+Thunder from Reuniclus and 2HKOing back, also two shotting Musharna and OHKOing Goth, plus a cameo from Gigalith to take down Sigilyph
Shauntal: Stoutland beat Cofagigus and most of Golurk, Seismitoad cleaning up the scraps. Serperior pushed through Jellicent, and Seismitoad and Gigalith teamed up to take down Chandelure - Gigalith probably could have done this solo if I'd picked it first..
N: Zekrom/Reshiram stuff, Gigalith picked Reshi off after a Hyper Beam. Klinklang was met with Seismitoad except it was actually Zoroark which ended up being a credit to the Toad as Focus Blast wasn't even a 2HKO against it, some Poison Touch Drain Punches later and Zoroark fell. Klinklang proper then came and
couldn't touch Toad was able to kill it with Hyper Beam from 25%. This afforded Serperior the chance to come in and set up but it also fell because Metal Sound and steel type > Grass STAB. Gigalith cleaned up after the Hyper Beam. Carracosta came next, met by Stoutland and Stoutland was unable to 2HKO with a Work Up boosted Dig and fell to Carracosta, Escavalier coming in for the clean up KO. Archeops next, arguably the biggest threat, was met by Gigalith who promptly sat the bird back down (no idea what it did, Quick Claw procced). Last up was Vanilluxe who could do nothing against Escavalier.
Ghetsis: Stoutland > Cofagrigus (though it tanked a +4 Crunch...). Stoutland > Hydreigon. Escavalier and Zekrom (and Seismitoad) did a switch dance until Hydreigon ran out of Fire Blast PP, then Escavalier smashed the Hydra down (sidenote, I got crit so many times by this Hydra). Gigalith almost > Bouffalant but not quite thanks to another crit, Seismitoad cleans up. Enemy Seismitoad comes in and kills before I can Grass Knot (ANOTHER crit, p sure I was in a living range), Escavalier gets up two Revives before drying to yet ANOTHER crit on a rain boosted Muddy Water, now Serperior can come in and one shot with Leaf Blade. Eelektross next and my Toad is down so Serperior sets up a Seed before going to Gigalith because ow Acrobatics hurts. Stone Edge promptly dispatches the Eelektross. Bisharp is next and things need Reviving to take it, but first Serperior throws out a Leech Seed. Turns out Bisharp doesn't have Iron Head so Gigalith just sits it down with Bulldoze instead of Reviving. GG Ghetsis.
League MVPs: Escavalier, Serperior, Gigalith, in that order. All three played pivotal roles with their bulk and typing and power/sustainability being major assets. Seismitoad did a little bit more than Stoutland (designated Cofagrigus bitch) who did more than Swoobat (did nothing).
Now, about the mons themselves (as a note on levels and experience, I did not do any backtracking at all but I did consistently equip my lead with the Lucky Egg and fought all trainers on the direct paths and expected side areas)
Snivy:
Strong B tier with and outside case for A. Always exceptionally bulky meant that it was a rare situation where it was unable to contribute in some way. Early in the game Leaf Tornado and reasonable Normal attack power / less bulky Grass resists meant that it was something of a power house tank, proven in the fights against Cilan and Lenora. By Serperior the offensive margins had fallen off meaning it was relegated to a bulky set up attacker in big fights but it pulled off that role with aplomb, being solely responsible for a victory vs Marshal and a key player vs Grimsley. Not the most efficient entry because of it's lesser power and limited coverage, but definitely a valuable member of the team.
Serperior lv 51 @ Big Root: Leaf Blade / Leech Seed / Return / Coil
154 / 92 (blech...) / 116 / 98 / 118 / 142 (fast tanky mofo, another 20 points in attack would have made a world of difference)
Lillipup:
On the A/B borderline for me, probably wouldn't fuss with it in A because I know mine had some pretty shit IVs. Starts off as dominant through the Lillipup phase and tailed off to simply consistently useful. Power issues kept it from being able to OHKO a lot of things so it never ended up being a world beater and ended up more as a mon I could throw into any situation and be reasonably comfortable with where things would end up. Intimidate was a big asset. Maybe fits better in B just because it doesn't really have any specifically great gym or E4 matchups (barring movepool abuse w/ Substitute on Chauntal)
Stoutland lv 46 @ Scope Lens: Return / Crunch / Dig / Work Up
138 / 108 (meh...) / 93 / 57 / 93 / 97 (slightly above average across the board I guess?)
Woobat: Okay early game, fantastic middle game, tails off in the late middle, shit end game once the garbage tier stats finally catch up with it. Woobat itself performed fine for me, it was frail but comes at a point where it gets consistently favourable matchups to compensate (Fightings and Bugs and Grasses aplenty). As I detailed in my run, my Woobat evolved immediately after the Burgh fight and from this point Swoobat was a major force and the best member of my team, maintaining this strength up until roughly Clay. At the early 30s it started to tail off and by the fight with Iris it was no longer able to contribute to any major fights (or most trainer fights) in any meaningful way. I had been of the belief that it should rise to C for its performance most of the way through, but it unfortunately puts up a massive zero in the end game so
D tier is appropriate.
Swoobat lv 46 @ Amulet Coin: Psychic / Air Slash / Calm Mind / Fly
125 / 74 / 79 / 83 (oh no...) / 59 (oh no...) / 127 (yikes. what a mess. no wonder it fell off in the end game)
Roggenrola (Trade): Very impressive showing. As I've detailed before, the Roggenrola phase took a bit of care, it performed fine on its own but needed to be held back for appropriate matchups. Once it evolved into Boldore however it became a beast with some major stat increases, it was both powerful and strong, to say nothing that you can evolve it immediately if you choose. Burgh was a stomp, and Elesa would have been had I let it fight the Emolgas. When I evolved it into Gigalith at Skyla it turned into a monster. Incredibly powerful, incredibly bulky, the singular downside was its slow speed making it annoying to lead with when running in the wild. Dumpstered Skyla, would have been able to dumpster Brycen, would have performed well against Iris, and effectively answered some dangerous threats in the E4 run (Archeops, Chandelure, and Sigilyph as most notable).
Trade variant is A tier for me, B at the minimum.
Gigalith lv 49 @ Quick Claw: Rock Slide / Strength / Bulldoze / Stone Edge
150 / 160 (woo!) / 136 / 72 / 87 / 47 (literal definition of a physical tank, spdef isn't too bad either tbh)
Tympole: Pros and cons to this one. Starts off self-sufficient with Bubblebeam offsetting weak offenses, and evolves into Palpitoad at an appropriate time, just in time to completely invalidate both Elesa and Clay. Offensive capacity falls off after this point and never really recovers, but the bulk remains and it's one of the best available, with excellent coverage as well once it evolves into Seismitoad. Toad had some use in the E4+, Grimsley's Krook and Bisharp are premium targets, as is Ghetsis's Eelektross and N's Klinklang. Overall I enjoyed using it but I just didn't feel too many situations where I wanted to use it, almost every time the decision to use it was based on its phenomenal bulk and defensive typing rather than anything it could do offensively.
On the B/C borderline, based on its E4 performance I would lean to C, but would lean to B for its middle game performance.
Seismitoad lv 48 @ Expert Belt w/ Poison Touch: Surf / Grass Knot / Dig / Drain Punch
175 (!!!) / 90 (blech...) / 100 / 96 / 78 / 88 (such a fat boi!)
Karrablast (Trade): Won't go into too much depth on this after the recent discussion, but I really couldn't have asked for more from a late game addition. Give it a tiny bit of patience, to Icirrus if you can't evolve it immediately, and you get one of the best end-game beaters available. Beats Sklya, destroys Brycen, beats Iris, destroys Caitlin, beats Grimsley, and is incredibly useful both offensively and defensively against both N and Ghetsis, particularly as a reliable way to beat Ghetsis's Hydreigon (since the party Dragon aka Fire resist is forced).
People will argue it to B, and that's reasonable, but it's A in my heart. A lot of the same reasoning as to why Lanturn is justified as A tier for me in Emerald
Merritt. Extra note is that mine was a Calm nature so I actually lost out on a lot of power too, in exchange for slightly better special bulk.
Escavalier lv 48 @ Rocky Helmet: Iron Head / X-Scissor / Slash / Rock Smash
139 / 129 / 109 / 81 / 117 / 35 (what a beast, surpassing Serperior in defenses and behind only Gigalith in offenses)