Why is Conflux often banned in tournaments?

I've heard many times that Conflux is an overpowered town. Some of its strengths are indeed a thing to consider:

Phoenixes are good 7th level creatures (when upgraded), creatures of levels 1-3 are also good. However, many other towns also have strong creatures, for example, Castle with its also overall strong creature line.
A lot of units are immune to Armageddon, making the Drageddon tactic strong as Conflux and weak against Conflux. However, I didn't see Armageddon as a popular spell. Finding the Grail, which is the only way to get Armageddon in Conflux, is also rare, and probably indeed deserves a decent reward.
Elementals are immune to Mind spells and to Bad Morale.
Conflux caster heroes are strong, especially some of them, like Luna. Still, other towns also have heroes that are too good and hence banned.
Magic University allows getting the desired magic schools quicker if gold is available.

However, just as many other cities, it has its downsides:

While Elementals are unaffected by negative morale, they are also unaffected when it is positive (like the Undead).
There are no ranged units without upgrades, which can take time.
Elementals cannot be resurrected and have vulnerabilities to certain spells.
Level 4-6 units are not so good.
Conflux is generally rather expensive. Most of its strengths don't pop up unless a lot of resources are available.
While it is easy to clear the map with some of the Conflux tactics, this city is vulnerable to an early rush, especially when resources are scarce.

A similar list of pros and cons could be written for any town in the game. This town has never appeared really overpowered to me, yet it is banned in tournaments when possible. But I am not a professional player, so I am asking:

What makes this town overpowered rather than just an interesting addition to the game?