I absolutely HATE quagsire to the point that I never, ever will run him again. Godawful defenses, I'd rather deal with Clefable or a priority stall pokemon carrying mach punch (kind of conkledurr with AV imo).
What I've started to do is just invest one pokemon that has a fantastic speed tier and work it into a stall pokemon. Pokemon like
jirachi, latias, tornadus-t, thundy-i, Starmie, tentacruel all have a good bit of utility/bulk to go along with that 100+ speed tier. It is a bit off the traditional beaten path for stall, but it also gives me the opportunity to work outside the box a bit. And I'm not breaking the mold too badly by still looking for acceptable bulk and utility, I simply lower the standards in search of speed. Even
azelf,
delphox (who has a fantastic support movepool and wish recovery),
kyurem (missed the tier, but has phazing and a good amount of bulk along with roost),
Zygarde (Rest, glare, stab/stab...Limited support, fantastic bulk),
Cobalion (excellent defense, excellent support move pool, my candidate for best lower tier stall support),
mismagius and of course
zapdos also have excellent reasons to use them for their speed tiering.
Last gen, I didn't care much for speed but this generation, there is just way too many issues with countering everything. If you can build a fantastic stall team in five pokemon (which frankly has been the Dreadnoughts all along... five pokes and one that just can't find a spot) and you have a diverse amount of specific pokemon you'd like to make sure aren't going to harm you, going with a faster pokemon to just not let that pokemon hit you might be ideal. As you mentioned previously to me, Nysyr, you said stall lacks diversity at times because you're limited in how many ways you can counter a pokemon. This is probably the best way to alleviate that, blurring the lines between a revenge killer and a stall pokemon, basically making a fail-safe. I don't like it much as an ideology to have to sacrifice pokemon, but specific calculations for bulk and drastically specified ev spreads can be made with some of these to maybe even form them into a fast counter, being able to maybe just take one hit but OHKO back.
Mega venu is the easiest way to check/counter (with eq on venu) Mega Lucario physical variants, and if you don't have him on your team you should at least have Slowbro. The main reason to use Mega venu is to have something to sponge weaker knockoff spam from stuff like Mandibuzz and Gliscor who are otherwise huge dicks to try and break for stall. He also is an amazing trick sponge for stuff like scarf Rotom-W, who otherwise you would have to sac a poke to not get boned by it.
IMO something like: Chansey/MVenu/Mandibuzz(with foul play or whirlwind at the minimum) is a good place to start for a stall team.
I like your thinking here. Very good start indeed. Unfortunately, you still need an answer for mega pinsir and that generally comes with rotom-wash, skarm or zapdos.