Alasie and Magni are two heroes who will probably fit better into that defensive roll spot. You could give yourself some time to try your chances of obtaining another hero from trainings or summons.
Nevertheless the opinions differ a lot about Aegir. Anchor graded him with an A for defensive raids and an A for the tanking spot. Richard also has an A for the tanking spot, but with Delilah and Gravemaker you already have two heroes who could fill that spot easily. I can’t really tell you more about Aegir, but this thread has everything you look for I guess: Can we discuss Aegir.
In short; most of the opinions say that he’s more useful for offensive raids. Having him at 3/70 will work just fine then. If you will not level him up:
Lianna - Gravemaker - Delilah - Khiona - Joon
Lianna - Delilah - Gravemaker - Khiona - Joon
If you’re running TC20('s) or regularly do summons then I would give it a little more time. If you want to try out Aegir, I would suggest pairing him up with Khiona. Possible order:
Lianna - Gravemaker - Aegir - Khiona - Joon
I don’t have any of the mentioned heroes, so there’s a chance I am wrong or forget something. No doubt that someone else will reply soon.