Smoke point is not the issue. You will be going way above the smoke point when seasoning. If you didn't the oil would stay as oil.
The thing to look at is iodine value which is what determines how much cross linking can occur. Flax seed is very high, but soy bean is just under.
I bought into the flaxseed oil camp and redid my cast iron but it isn't worth it to be honest. I paid over a dollar an ounce and it did a fantastic job but soybean oil can also do a fantastic job for MUCH cheaper and much less trouble finding and keeping the flaxseed oil which goes bad so fast...
There is a Vietnamese dish called ga ro ti that is basically roasted chicken made without an oven. First it is fried till browned then coconut soda (or coconut water) is added with the original marinade and reduced to create a glaze. Many today make it by frying in the pan then finishing in the...