- No real time to train aside from on Plasma Grunt here and there.
- Desert which has Darumakka lying around. Seeing as Petilil is too slow, no time to really grind either.
- Bug-type Gym where it gets slaughtered.
That's funny, because I'm looking at the trainer lists for Route 4 and the Desert Resort right now and am seeing exceedingly few things that Petilil absolutely cannot beat with Magical Leaf and a Growth or two.
Before that point, you have Castelia, which has plenty of trainers that Petilil does fine against. Inside the gym, there are a couple Dwebble that Petilil is more than capable of beating. And since Burgh's idea of what constitutes a Bug-type move is friggin' Struggle Bug, you can at least use Sleep Powder on Leavanny before switching it out.
- Can't really lead the party since it's slow as shit, which makes simple tasks like running away difficult.
This begs the question of why you aren't just using Repels instead of running.
- Electric-type Gym with Acrobatics flying rodents. You tell me the situation good sir.
Elesa's Emolgas have Aerial Ace, not Acrobatics. Also, by the time you meet Elesa you should at least be level 26 and evolved (indeed, it's possible you'll already have Quiver Dance), so you'll outspeed those rodents handily. Sleep Powder and a single Growth was enough to sweep for me (the rats took a 2HKO, but Giga Drain healed most of their damage). Aerial Ace shouldn't be too worrisome, since it's not a OHKO even with the weakness. Even though it's resisted, Elesa still loves spamming Volt Switch for some reason, which is nothing to fear. Flame Charge sucks, but +1 Giga Drain makes short work of Zebstrika.
Mega Drain is about a 3HKO and Magical Leaf means sacrificing one of your better moves for it.
Magical Leaf is way, way better than Synthesis. It's not "sacrificing one of your better moves", it's sacrificing a move that sucks (especially when Fresh Water >>>> Synthesis).
Giga Drain + Quiver Dance is also a mile stretch away,
Not really. You can easily have both coming out of Nimbasa, which is only a couple towns past where you pick it up. Since it has decent offenses before that point, it's not like it's a dead slot until then, either.
and its situation isn't arguably better since the next two Gyms have Super Effective moves on it
Two Quiver Dances with Liligant's amazing SpA and Speed is enough to sweep pretty much anything without ever taking a hit (assuming Sleep Powder hits). Admittedly the Flying Gym isn't great for her, but even then you need to keep in mind that most of the Gym is slower than her and has pathetically low SpD (not to mention the Duckletts running around, who are not fond of taking a Giga Drain to the face).
and the final Gym having a bunch of Dragon-types.
I haven't gotten this far in my current Black run (where I'm using Liligant), but I seem to remember a huge portion of the Gym loving to spam Dragon Dance. This gives you a ton of extra time to set up, which goes a long way towards making up for the resists.
Now granted you can Sleep Powder -> Quiver Dance -> Sweep on some Pokemon,
It's more than "some". Most Pokemon simply can't handle 75 Power STABs coming off of a 31 IV'd, positive natured, 110 Base SpA at +1 or +2.
but Ice-type Gym for example has Frost Breath which cuts right through the SpD boost.
This assumes that Brycen will ever get a hit in. I'll admit that this isn't an ideal place for Liligant, either, but I can't imagine it's an impossible situation.
The other two Gyms are a different story of course,
And that story is? It has neutral coverage on both and is weak to neither, so it should do fine. That might have been your point, though.
though it probably isn't AS good in the E4 as people are trying to throw me into (I haven't actually gotten to E4 with Joltik on my team).
While he didn't trivialize the League (keep in mind this was the run where I was around 47 going in), he doesn't have very many bad matchups, either. Of the Elite 4, the only one I would completely not suggest him for is Marshal (what with all the Stone Edges), but the others are fine. N noticeably uses two Pokemon weak to Electricity and another that's weak to Bug. Ghetsis isn't a great matchup, but that's the fight where you really, really want to find some way to set up and sweep anyways (Scrafty and Excadrill being perfect examples of that).
Well then, I guess I may change my mind. Who's hearing Mid Joltik?
Honestly, I'd consider it right on the line between High and Upper Mid. The fact that it's somewhat mediocre coming out of the gates does it no favors, but it's a wonderful member of the team after that. I'd lean towards High, though.
Incidentally, I'd argue about the same thing for Petilil. She's not amazing coming out of the gate, but she never felt like too much of a burden, especially with Sleep Powder. Once she evolves, she gets the best setup move in game, which really plays nicely with her huge SpA, high Speed, and decent STAB (or amazing STAB right about the time you hit the Elite 4). The Gyms don't let her shine very much, but every other random trainer just folds to her, and the League is actually fairly generous about giving her time to set up. Definitely at least Upper Mid material, High if we aren't being too incredibly exclusive.