Asking for a friend, is it bad that they are struggling to beat Chaos 0 Lab difficulty 4 with nightmare mode on?

So that friend is account level 48 with the characters they use at level 50 with partners at level 50. No five star partners. Potentials are mostly upgraded for their level. Memory fragments overall are quite trash, a couple yellows and some blues but with ok main stats and at level 3. Characters and partners they use are:

Dps: Mei Lin (Douglas) , Yuki (Douglas), Hugo (Rosaria)

Tank: Khalipe (Willheima)

Support: Rei (Arwen), Mika (Arwen)

Most runs are ended by the dreaded Vagina Bat near the end. Few are ended by the exterior last boss with debuffs on from dimensional tunnel. I don't know if zero system upgrades carry over to Lab 0 but they've only done zero system once so they barely have anything from that.

So is it reasonable that they are struggling or are they just cooked at the game? Granted they absolutely love the difficulty and aren't discouraged at all. But are they cooked?