Calling its ability 'essentially Levitate/Corrosion' seems utterly bizarre to me. Firstly, it also suppresses the abilities of all enemy fusions, which against many abilities is a huge damage decrease (particularly for Guts users who effectively have their damage cut to 1/3 compared to usual if using Flame Orb). Seriously, ability suppression is huge in FE, you can't just ignore it. The ability also prevents Ground types from switching into its Electric moves which makes Volt Switch unblockable (and it's got a decent bit of power), and it can burn literally anything with Will-O-Wisp and then Pain Split back up from there thanks to low base HP. If it sets Toxic Spikes then anything that switches onto the field afterwards will be poisoned even if it's Steel, Flying, Levitating or wearing Heavy-Duty Boots (the ability does suppress ALL immunities so those definitely count imo) I'll admit that the bulk isn't as good as it looks and the recovery is a pain, but you're underselling the ability a bit there :PRotom-Wheeze is wack, having about 85/85/85 bulk which is pretty mediocre. The only thing distinguishing it is its good defensive typing and essentially Levitate/Corrosion ability, which I doubt makes up for its lack of reliable recovery.
Boomer's main set is, yes, a Choice Scarf revenge killing set, but it could also theoretically use a Shift Gear set also as a cleaner with its snowballing ability.
Tapu Apex is pretty dumb, it's fat as hell and instantly sets its opponents on a timer.
Terror is a Ferrothorn. No one's going to Mach Punch a Ferrothorn, they'll just Close Combat it.
Xyerom-D is overrated in my opinion, people talk about huge mixed offenses but it's 115??? Can only see this working with a janky Crocune set really.
Crayquazant is also overrated, it pretty much dies from any attack but also doesn't have that much offensive presence either. Mega is ok I guess.
edit: also for Crayquazant remember it can still hold an item while using its mega