Question

Slurp! While Super Rare units are good, EX characters, who are counter-units against ancient enemies, become essential starting from the new Legend stages, hmm! Especially, drop characters can perform even better than Super Rares once they reach their third evolution, gaining bonus damage against super-beasts and curse immunity. Considering the 4-star stage restrictions, nurturing them in advance is a solid strategy!

Dunno..

It depends on which Super Rare, and which EX character you have. For example, Kakumushi sometimes gets used because its Instincts add an explosion effect, and the others also become quite usable with their third evolution adding anti-Ancient damage. However, they're not as good as Super Rares, and they require Ancient Catfruit... I'd suggest just pushing through with Super Rares and trying EX characters if you're really stuck. Personally, I think Musashi is quite useful due to its long attack range.

Super Rare units can do it all, but good EX units are still used.

There are drop characters you get from Shinra, and against ancient types, they're better than most Ultra Rare units.

The drones and such that you get from Shinra are as good as Ultra Rare units.

Well, things like the Ancient Tree Kingdom are used a lot.