Terrakion: I was too lazy to catch it and caught it in a Master Ball (there are no roamers anyway) and it does pull its weight, but it is a bit awkward at times. Rock Slide and Sacred Sword seem to both fail to KO a lot of things (+2 Sacred Sword missed the KO on Haxorus wtf) and, as a result, it often dies in the process. I got one with a shitty Speed IV, which also meant I couldn't solo Iris with it (it might well be 0, lol). Still, it does do a good deal of work and, provided you don't get a crappy one like mine, can sweep a good bit of the Elite Four, including Iris. I'm not sure how to rank it, but I think I'd stick it in Mid.
Traded Cottonee: I was surprised to learn that after the initial shit stage with Cottonee (the little arse that trades it to you deletes Leech Seed wtf), it actually evolves into something fairly decent. Giga Drain / Charm / Psychic / Leech Seed works pretty well through most of the game, it levels up quickly, and has an oddly high attacking prowess. It's honestly comparable to normal Lilligant.
Elekid: As I've stated above, throughout the whole of the game, I ran this with Eviolite. Early on, you get by with Thundershock, later Electro Ball; I kept both Electro Ball and Thunderbolt since Electabuzz doesn't really have much else anyway outside of Psychic and tutorable Signal Beam. Electro Ball is actually pretty nice since using Thunder Wave means it is nearly always (barring Jolteon and the like) a 150 BP STAB attack. Eviolite gives it surprising bulk that I tend to underestimate; it resulted in my win against Iris, really. Thunder Wave has a static utility throughout most of the game. It's not absolutely the strongest mon, but it's good enough, really. Goes in Mid.
(Mareep does not deserve high; it is objectively worse than Electabuzz and not able to actually use Electro Ball properly to begin with. Should be stuck in Mid if anything).
Pinsir: I had nothing to really go against Elesa then realized that this thing learns Dig. Well, that was a short gym battle. It learns STAB X-Scissor then just kind of... falls off later on. All of its moves have pitiful BP, with not a single one (outside of superpower) going over 80 BP. In this respect, it really looks inferior to Heracross, which, although it has to wait for X-Scissor, gets a consistent STAB in Brick Break as early and gets the slightly weaker Bug Bite if you want to tutor it. Anyway, at the end it's ok, but not spectacular. I tried to sweep Caitlin with it and then she crit OHKOed it with Sigilyph (though I think it may have KOed regardless). Swords Dance is nice on any Pokemon and Pinsir is no exception. Mid.
Skarmory: Skarmory wishes it lived in RSE-land, a land where the mystical Roar TM comes before (or is it after?) the fourth gym. Instead, it really gets nothing until Seigaha City, where it gets something wonderful - Roost, and for a meager 6 Yellow Shards. In the leadup to Victory Road, it gets the Roar TM and finally becomes really (tbh) funny. It can sweep some teams just by abusing Spikes + Roar. It's really sad that it doesn't get Roar or Whirlwind earlier; they'd fill up an empty slot that Steel Wing just kind of... "occupies" for most of the game. At the end, it's a really good wall that is nigh unbreakable. It can wall your rival's Afrobull, for example, which is impressive considering it has Wild Charge, which 2HKOes it... if you don't Roost. Mid, actually.