Eh it depends. Storywise I'd say yes, Part 3 ramps up in insanity and I recommend it for the juxtaposition alone.
Gameplaywise no, god no, fuck no. I'm sorry Part 3 goes from being comfortable dificultywise early on then the longer you go it becomes extremely tedious very fast. Enemies start packing millions upon billions upon sextillions of hp (I'm deadass no hyperbole THE final boss has hp in the Octillions) and once the chaos route starts will Atomize you if you're not grinding and exploiting mechanics introduced in part 3 thanks to chaos jobs and new monsters. Luka pretty much goes from a meh party member that you can ignore to borderline necessary if you want shit to get done by virtue of him being the mc and therefore THE permanent party member. God forbids your team is made of story characters of which a decent chunk will be temporarily removed once you start it. It doesn't matter who from, the succubus sisters, Alice, Illias, Sonya is just gone for 85% of the route lol, to the imps and mother fucking Lazarus they will be gone and getting them back can take several hours of grinding, searching, fucking around and finding out that you just cant get someone right now.
I'd say if you have already started part 3 or spent several hours of grinding in previous parts commit to it. Your NG+ grinding helps you keep up as grinding becomes necessary at the tail end of Part 3 save yourself the headache. Especially given the penultimate dungeon has you arrange 3 different teams of 6 so you better fucking have a rotating cast of monsters for the trip or you're going to want to die inside as everything can and will one shot you as you're treading on thin ice every other encounter. I regret ignoring Illias despite the fact that she sucks.
Otherwise you're fine just starting over. You can also have a best of both worlds situation resetting your party members with the reaper during a NG+ run.
Edit: just to preface if Part 3 gets too bs, the game does throw you a bone but it's baseically god mode and even then I still wanted to use mtool.
If you check the patches folder you might find a few mods that are outdated and should be deleted. Anything that has to do with the Library get rid of. I don't remember what but check out this
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and you can probably figure out what needs to go and what can stay.