It's basically just a straight up nerf from Legion. At least in Legion we can choose from 6 talents, in BfA it's only 4.
On top of that, you really only have 3 to play around with since the top one is just like we have on live with the 3 CC breaker choices.
So that leaves us 3 to choose from the pool. Well, so far every class I've played pretty much uses the 3 best talents from the pool at all times. Maybe there's 1 you can switch depending on whether you are going against a caster or melee team, but for the most part, you just stick with the 3 best ones.
For instance, for my Veng DH, I'm GOING TO GET DEMONIC TRAMPLE. Always. That is just a given. There is just no scenario where I wouldn't want this godly catch up/get away ability. I'll also want my Infernal Crash snare since I have no other snares (the DS snare talent is trash for PvP and you'll always want to go for longer ranged leap with shorter CD talent). The 3rd talent, I can get Solitude if I'm out doors doing WPvP solo or maybe cleansed by fire/Jagged Spikes if I'm fighting casters or melees. That's it. All the other talents are TRAAAAAAAAAAASH.
Same with my WW. the FoF stun is MANDATORY. Grapple Weapon is MANDATORY. The 3rd slot you can play with a bit, maybe. You're still gonna want to get Disabling Reach for like 90% of instances, but I can see maybe switching to Fort Brew for some. Rest are TRAAAAAAAAAAASH.