300 heavenly dew for 200 aether, OR 500 dew for lv 2 defense fortress?

Hmm, at this rate, I'd say the Fort. I didn't pick it and I'm super boned rn on defense rn since my fort is lvl 2 (while my enemies have lvl 3)

200 Aether, easy. it's nearly impossible defending against units that get a +8 bonus to all stats, 4 won't make much of a difference. Combine that with the fact that AI is kinda bad, its easy to take down AI teams even without a boost.

I went Aether last season and paid off starting with 200 this one. I think most recommend aether first as it affects how many matches you can run for offense. Defense is not as vital yet since there's no loss in lift yet. Though that will be very soon. I don't think there are ironed out try-and-true strategies for good defense teams yet. Defensive wins also don't net anything (like rewards). So as long as you are still defeating a few characters, you are still applying some pressure on defense. If you still struggle to kill a single unit, then likely an issue with your team, map layout or something else.