Okay, if you're including boss fights, there are a lot of boss fights in other games that just go on a bit too long, too. It's just for the sake of difficulty levels. For people who aren't completley leveled up, these fights become difficult, too.

As for getting bored with combat, I did, just because every fight was virtually the same. Chain break the enemy juggle him to death. Until later when you fight the big things and it becomes: Make Vanille the lead, summon, spam death. I rarely found myself doing anything differently and watching my party juggle enemies just reminded me of Star Ocean 2 where juggling is pretty much your guaranteed strategy for victory, or the fact this combat system is pretty much Xenosaga Episode 2's combat system (though in X2 you can also smash enemies into the ground and combo additional smashes) so its not like I can't get this fix from other games that predate it, sometimes almost by ten years, but with the added bonus of having control over my party. I'm not even going to get into how much this game recycles enemy types. Juggling Behemoths does lose its luster when they are regular mooks that show up every other dungeon.
Doing this when you have other enemies out there that are still alive can end badly depending on the enemy, but oh well. You're right, I suppose, that it is a strategy that works well for most enemies. But then, if you look at almost every other FF, there is a familiar strategy that works on all enemies, too. For me, it went like this: Attack, Attack, Attack, Attack, Attack, Attack, Attack, Attack, victory.

As for the enemy system, they are actually your third party member from what I've gathered, each one being specifically designed for a paradigm role. I'm thinking its something like having a Behemoth as a Commando, a Goo monster as a Ravager, or a Machine as a Sentinel. At least that is my understanding, so its not so much a summon system as much as its paradigm shifting with your monster determined by what you need your third Role to be. I'm more concerned to see if any of the returning cast will be playable besides Lightning, cause this system pretty much sets up all you need for a three man band.
Ooh, that sounds great. Where did you hear that, out of curiosity? I've not seen any info about this outside of the magazine. Not sure if I missed something in there... but yeah, that sounds pretty cool =]