I think it’s okay to have different opinions on this stuff - different defensive setups can succeed in different ways.
My personal preference on defence is always to start by choosing the best available tank then build a rainbow team around it, mostly omitting snipers and using AOE heroes instead. I always like to include a healer.
It’s worth me noting that I don’t know enough about Ameonna to make an informed comment about her, so I’ve basically pretended she’s not there.
So having said all this, I really like OP’s proposed defensive team of:
Azlar, Li Xiu, Aegir (not Richard), Kashrek, Sartana
The obvious weakness is Kashrek’s limited heal. Given the heroes available, the way to fix that would be to use Rigard as your healer instead, omitting Sartana and instead using Caedmon. In terms of arrangement, I’d propose:
Li Xiu, Rigard, Aegir, Azlar, Caedmon
That team would he tougher to kill, I think, because of Rigard’s considerably superior special, but you would be sacrificing significant firepower in using Caedmon instead of Sartana, and both are (sadly) snipers. Caedmon’s dispel might be useful, I suppose, but as ever with the AI, it would certainly be used at the wrong time.
I dont know which I would prefer, the defence team proposed in the OP, or that one.