Devotions are intertwined with your mastery/skill choices and overall balance/gear etc… what makes you think it’s less complicated? They go in tossing new stuff in there then the stuff outside it has to reflect it as well.
Manticore should at least get bonuses to bleed on par with its bonuses to acid. The only paths that are seriously going to consider it are bleed builds without Nightblade, since purple/green is on the way to their T2 RR constellation and T3. Since manticores also do bleed damage in-game, it’s thematically fitting too.