Artificial Difficulty

[Reynhart]

A fight based on a scripted rotation can even be done by someone with the reflexes of a snail, the only thing you might need is just more tries.

And on each try, you will improve yourself until you manage to pull it off perfectly. That's one kind of difficulty. Something we see all the time in rythm games, for example.

Extend the length of the fights and this problem is instantly solved.

Then you'd also need to restrict some mechanics. If Titan Ex decides to spam Double Gaols, you're screwed...
If tankbusters happen every 15 seconds, your tank will surely die, too...

But, a fight where each attack has its own cooldown, and where the boss can chose whatever ability he wants that is not on cooldown, could be very fun and interesting.