First, this opinion is only mine. The passives of the bosses are too specific, as if you need to prepare a team with the objective to beat it, like Darkest Dungeons or similar games, and that's not fun for me. I've enjoyed, and replayed, the previous games but my only problem here are the passives of the bosses. 

There are people who enjoy challenges, but I don't. Since just removing them could be too extreme for some, maybe place a checkbox under the dificulty setting enabling "challenge mode" with the passives and giving unique rewards for beating them.

Bosses aren't that difficult that you can't just overpower them with sufficiently strong team regardless of specific builds, at least early ones.

I never plan character or weapon builds to counter specific bosses. Well maybe Kuro's god fight.

Leon's fight was the most difficult for me due to unable to get later gears and it hits harder than the boss in Kuro's last mission boss when he rages.   Previous version allows party to choose random class for some obscure bonus, now the math is much tighter and even with armor maximized enemies may still one shot characters.  Enemies are getting to 300+ attack around dream maze level 25 with tons of  hp. Also dodge tank is barely functionable now with enemies often having very high to hit bonus.  In older version player can bring some lesser NPCs like the princess and still do reasonably well, now party has to be much more optimized just to run.  Tons of enemies have def/mdf too high to be damaged, player must debuff first and often only one damage type would work.

I like the more challenging fights! Strive is so much more then an good'ol h-game at this point.
Please keep the difficulty.
I defeated him first time. He is strong, but it was not that big of a deal with a full party.

Yea, i play the game causally. The prior versions i enjoyed as i wasnt required to pull out advance calculus t analyze how to beat a boss, but now i have to build a specific group for each boss, and there are more of them now. Sorry, looking like i wont be making it through act 2 anymore. This isnt what i signed up for and its just not fun. May check back later if things improve.

I gotta admit, I dropped a few quests entirely simply because of the boss fights were insane; Jean's final (?) route boss is absolute bull if she manages to drop either your casters or melee specialists out-of-order with her party-wide attacks, and I can't even beat Greg's second coming since he just tops himself up before launching another ten or so attacks on my party *per turn*, completely wiping my caster line before they even get a turn to act, and they're all sporting at least Mithril-level gear and (hopefully) reasonable class lists. And I'm not even looking to trying to finish Kuro's quest after getting soundly beaten by the previous two boss encounters. And as someone already mentioned, a dodge build rogue is just mincemeat since the AI gets insane to-hit bonuses.

Not sure if there's any way to beef up to sufficient XP (roughly 3k for main) or power levels anymore since advancement of stats is now land-locked to turning in slavery missions, which yield only so many tokens that can be used to buff your mainliners, but never enough for the whole party, leaving their leveling sub-par while trying to turn in quests.