[Wendigo]

I concur with Patrik.

Jotun's biggest weakness is the lack of random picks in fire/earth/air.
Getting air on the pretender gives you among others access to air magic, wards vs air, protection vs missiles & protection vs fliers...all stuff you do not have.
Your cold dominion & your air proficiency also offer a degree of protection vs fire.

Getting astral on your pretender doesn't help compensate for this, and in addition makes your other vulnerability (being a 2nd tier astral nation) even bigger, as now both your battle mages & your pretender are vulnerable to Magic duel. This will not hurt you in SP, but can easily doom you in MP.

While you could get a high lv of astral to avoid this vulnerability a Wyrm doesn't cut it as a SC in the end game, so investing in high astral would not be a good idea IMO. Non humanoid pretenders can barely stand vs fully equipped humanoid ones when Const4+ is researched, much less when artifacts come into play.
The Wyrm works as a relatively expendable, easy to use, forgivable with mistakes Pretender for early expansion both in land & seas. Trying to turn the critter into something else with more than some token magic is a waste of design points IMO.