I'd not call it "lucky"; the bulette managed to kill two character in that fight, but it also angered the hook horrors in the process. :P
But I think Larian should add different difficulty options in the EA for people to playtest before the full release. The difficulty doesn't seem consistent.
You know it's not even really about difficulty. The minotaurs are plenty difficult without being able to jump 80 feet. Same with the hook horror battle, 4 hook horrors and a mage, is plenty difficult without letting giving hook horrors jump attacks that can one shot anyone in the party, the bulette is plenty difficult without being able to spit AOE acid. Phase spiders are plenty difficult without giving them the ludicrous ability to spit poison.
The jumping/disengaging from combat is also completely broken, and makes melee combat 2nd class to any form of ranged combat, there's literally no benefit to trying to tie up someone in melee when they can jump out without penalty or risk, and that goes for enemies and party members.
it's almost as if Larian is trying to make the only viable tactic in the games to be using the DOS features they've thrown in with AOE/surface spam, along with mega-jump and 'push FTW'.