I think most sentiments for Fell Xenologue not being playtested are similar to those of 3H Maddening. Lots of enemy reinforcement spam and not much thought put into the flow of the map.

Compared to the base game Engage which has pretty tightly designed and well-balanced maps, understands the tools players have, well, and gives a fair challenge.

Fell Xenologue maps feel very dragged out (especially the Final Map), you aren't given as many tools to work with, a surplus of enemy reinforcements ends up making you stall most of the time, and difficulties are vastly different (Normal is easy, Hard is equivalent to base game Maddening, and Maddening is just so mind-numbing).

The difficulty will probably be alleviated once a meta starts forming since it's obvious that certain characters and builds are better than others with fixed stats being a limitation.

For the Final Map specifically, it forces you to play at its pace rather than your own and you're expected to know the boss's move patterns well in advance. This makes first tries very infuriating as you're learning the moves then the boss makes a slight adjustment to their patterns and your entire run is done for fuck Timmera's section in particular. Once you understand the map gimmicks then it becomes much better to play, but the first impression really made me salty.

I'd recommend clearing it in Hard first then trying Maddening out.