I really don't think Speed ties should be a reason for banning things... top threats in LC are always going to be fast Pokemon since everything is so HO. The problem with Misdreavus, is that you patch a hole and another one opens up, meaning if you check some things by carrying Berry Juice, Taunt or HP Fighting, you end up losing to other things, but then again, the issue at hand is that you carry a dedicated check to Misdreavus and it gets fucked over by one of Misdreavus' options, you could be in a lot of trouble, losing a lot of momentum or having your check beat completely, forcing you to either run a secondary check or work your way around her in the battle if your check gets crippled or something. Sadly, that point is heavily luck-reliant since Swirlix used to do this, except the penalty was getting your whole team swept because of a different set, whereas Misdreavus will punish you with losing your check and another Pokemon or sometimes it may be able to sweep you, if it gets the opportunity (Unless you set up a win condition before she pops up).
I heard someone mentioned Grass types being hurt by Fletchling's presence, and that is completely preposterous. Chespin is not saying in on ANY Flying-type ever. Foongus is already really good. Ferroseed doesn't care about Fletchling, and has the ability to hurt it with Iron Barbs unless it has Overheat. Cottonee is still amazing support and it can Memento in Fletchling's face as it tries to use Acrobatics or U-turn, leaving it as setup fodder for your sweeper. The only grass type truly hurt by Fletchling's presence is Snover because... Snover runs a Choice Scarf set, which even in the case of a 1v1 with Stealth Rock on both sides, Bulky Fletchling will be able to take Ice Shard from it and simply kill it with Acrobatics. Also, don't get me started on Fighting types because there's about 5 Fighting types that are very good in the LC metagame and Fletchling isn't deterring them from fulfilling their job.