Our team has so far managed to defeat all bosses except for Lord of Darkness, Omega and Psychic Sheep, and the ironic thing is that out of all the bosses we beat, I'd say Agiel is the hardest by far. Harder than Byatis, harder than Forgotten One, harder than Michael and even Laika. The only reason we can get by him easily is because there's a very simple strategy against him that gives you a 100% guaranteed victory. He doesn't even use half of his skills if you do it that way. If it wasn't for this strategy, many of our games would probably end with being unable to beat him.
I think it's a little sad that there's this really difficult and challenging boss that's right before bosses that are arguably easier to defeat, but there's this ONE strategy that makes him easy. I think it'd be much more interesting if Agiel was the last boss before Lord of Darkness and instead had some sort of resistance against said strategy (more spell damage reduction, less physical damage but a chance to crit/bash, or more true damage on hit, something like that), or at least wouldn't be prevented from using his problematic skills this way.
And if he's a later boss you're more likely to have some black or teal items to help you and have more of a chance to take him on directly. Funnily enough it's probably still perfectly balanced if he drops Heracles because that is a damn good item, usually much better than the ones we've gotten from Byatis and Forgotten One so far.
It's okay if things stay the way they are, I just find it a bit of a waste.