Is Conflux a broken castle?

But other Castles have their own balancing nuances...

Yes, that's true, but Conflux (and Necropolis, for that matter) are banned in online play for a reason. They still have an advantage.

Moner isn't the best sprinter (Gunnar, Kirr, Dessa)...

I think that in the first two weeks, Moner and Pasis will progress further than the others... :) Especially on the first day - these heroes (from the standard set) will run the furthest. And besides, Jelu is also a good starter.

Phoenixes are only restored after their final death in their group...

I meant the amount of hit points that these units have - an increase of 1000 HP per week (taking into account resurrection +20%). Where else can you find that? :)

IMHO, Conflux is overrated!

Everything is relative.