Has anyone tried a play through with max lvl characters (or at least a team of) on hard mode and enemy level cap removed.

could it make for a challenging playthrough or would i find myself blindly smashing my way through?

No, I haven't tried that.

Max level is relative, since you can transmigrate with the Fountain of Youth. If you haven't transmigrated, I'm sure it would depend very much on which characters you choose, because stats, not level, decides how powerful your characters are, and some characters have horrible stats (until transmigrated a few times).

probably best without transmigration as im searching for a way to play the game again with a challenge.

if no ones tried a playthrough with some lvl 99's and enemy level cap removed i may try it myself. or start a fresh game on hard with cap removed.

Level might be meaningless, but Stats absolutely cap. At which point you realize that a lot of characters become completely useless because their weapons and skills just aren't up to snuff.

Playing through again after that is really easy, but boring because all the enemy HP is so high, but they pose no threat to you.

I did once without transmigrated character.
Only Wil and the heroine seems able to hold on their own well enough from our initial party.
NG+ character is strong enough to overpower enemies though.

Bleh, I did it too with one or two fully transmigrated characters(iirc, I used Uya*1 and Melodiana*2) in case I got bored of the honestly stupidly tanky enemies. I also tried to stay away from using the NG+ characters but eh, they wouldn't have changed much (that and i think Lyphia/Evelyn have terrible skills and the non mascots take too much effort to bring to 99.)

Difficulty wise, it really wasn't worth it, enemies get significantly tankier over the levels but there's still a gigantic gap between enemies that know some form of prevail and every other enemy. Enemies just became much more of a chore to take out and most of them have hitpoints that require your characters to enter prevail to one round kill or 2-3 dedicated party members. Basically, the game is exactly the same as the speedier/more eva heavy characters are still basically god and anything that relies on "burst" damage to keep enemies away now doesn't work at all and requires someone in between them and enemies. In short, you slowed down the game dramatically with no real increase in difficulty.

This is probably most easily seen in that mission where Crayanne is saved and the ominous portals which feature stupidly large amounts of enemies. Be happy if you get through those maps in less than 5 hours. ._.;

I'd add that even the enemies that have prevail during the storyline missions are always spaced so far apart that the level 90 dungeon that features a fair number of them (that would be Advent Bay) is much more challenging overall.

*1 because I found Kohakuren to be all around better when given more levels
*2 because Elizasleyn feels like Melodiana V2.5 (much to my distaste ._., WRY is my spear user less powerful than a mage...)

At max level with his best weapon, Uya has an evade of like 75-85 or something. He's basically invincible.

At max level with their best weapons, most characters end up being pretty good. Bear in mind also that his best weapon only gives Evasion 3, something you can replicate on other characters with evasion salves up to level 5. Again, the only enemies that would hit either Evasion 3'd or AlertV'd characters are enemies with prevail making it a moot point in my opinion.

The real difference comes to proc-ing and maintaining prevail status as the bonus stats from that skill usually outweights better weapons once you reach level 70-ish. In this case, Kohakuren wins hands down. She only needs to drop to Earth Pipe to gain Prevail 3 whereas Uya has to drop to Hilfe Fang.

The real reason I found Kohakuren better than Uya later is due to the period of time between his event related class change(which still has caps) and his insanely high level 55 to unlock caps. That's a LOT of wasted levels as you'll probably max stats at level 45-ish at the latest whereas Kohakuren naturally has balanced growths and unlocks her caps slightly earlier than Uya.

This doesn't mean by any stretch of imagination that Uya is somehow a useless a character as he joins up at a time when you don't have many characters available to field and continues to become a very very powerful physical attacker (probably the only one that can consistently catch up to Beast Armor'd Yuela and work alongside her consistently as most of the other attackers are either slower mov wise or more frail.) for the rest of a normal game. He just gets gimped very very badly in post game content.

I heavily agreed with Haley. Haku is much better in a way that she has great int and mediocre str. In my first playthrough i found that Uya is much likely is Glass Cannon character, he has a good str but easily taken down by stronger enemy. He was sharing his usefulness with Sharty (has good critical rate and bloodsuck) later in the game as looter/hidden room searcher.