You only selectively included changes here, not the whole list... Here's the actual list of most recent changes to his W on the PBE right now:
Tahm Kench
Devour (W)
Champion spit lockout time after animation lowered from 1 to 0.25
[New] Allies can no longer release themselves from Devour early whole affected by enemy loss of control effects (stun, suppression, fear, etc)
Allied champion spit range lowered from 400 to 250
Devour damage changed from [100/135/170/205/240 (+5/7/9/11/13% target max health)] to [60/105/150/195/240 (+9/10/11/12/13% target max health)]
So they're making it harder for an allied Tahm to troll you I guess by lowering the lockout time, but punishing you so you can't get yourself out when he rescues you from CC, meaning you presumably have to have better coordination with your TK about when you want to be dropped, and they're also making it so it should be nearly impossible to spit an ally champion over walls with that range change.
Other than that, they're lowering the flat damage dealt by the ability, but buffing the %hp damage of the ability, but only in the early game. At rank 5, it's the exact same ability as it was before. Since they're lowering the flat damage by 40, and buffing the %hp damage by 4% at rank one, at that point in the game a target of his W needs to have 1000 HP or more for it to be an even change or a buff, so it makes his very early game a bit worse, and scales back up to where it was before, under most circumstances. Probably a buff against extreme health stackers like Sion or Cho, once you get a bit further into the game, especially seeing as most TK players don't max W first anyway. It's almost definitely a nerf to his very early laning in every case.
Overall I'm not sure if I see much of a point in most of the changes here, but your post does kinda skew them a bit since you didn't mention everything.