I always suggest playtesting in a one-shot or limited campaign. Existing campaigns are a lot of work, and a badly designed element introduced can really mess up the campaign (if not kill it). I've experienced this with homebrew stuff in the past, and nothing makes a player angry like nerfing their character mid-game.Is it not the point of UA to test subclasses. As they are. Then offer critique to balance them. Playtest them in other words.
Not when I have an ongoing game that can be wrecked. I learned that lesson with the Mystic.
Sounds like you got your future BBEG!Yes, but he also killed my campaign,

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.