For war defence, blue mid makes sense if the whole alliance can do it right… if not, put out your best and it’ll do better.
For raid defence, it makes very little sense - you’ve got a superb A grade tank but refusing to use it because you want to use a B- or C grade blue tank is borderline lunacy.
Of the three, Thorne is by far the most durable - neither Magni nor Isarnia (even with costume bonus!) can ever be considered anything but squishy… Great hero’s but simply not tanks.
Kunchen wing is useless - slow wings rarely fire and when they do it’s 95% of the time too late unless they’re resurrection hero’s. To make matters worse, healers in wings are easily ignored… And then it’s too late for them to change anything (again, unless they resurrect).
Slows need to be flank or tank… Speaking of which:
Isarnia (especially with costume bonus) can actually be pretty decent in flank if the tank is durable and either drops defence or raises attack (I get great results with her flanking a BK tank… She can be nasty on a Kunch tank too).
Elena is super squishy and doesn’t do enough when she does fire - not for defence IMHO.
Joon and Sartana are decent defenders, as is Magni but not at tank…
Once JF is levelled:
Domitia - Kadilen - Kunchen - Magni - Joon.
Dispel can be really useful, hence Domitia over Sartana (though try it both ways and see!!).
Kadilen and Magni are both better flanks than wings and Joon last because he’s a little squishy so best on the wing.