Thanks for giving it a try! I think there's a lot of room for experimentation in the shmup genre and I've been thinking about having a shmup with a strategy map/overworld for a while.
The upgrade screen was the last major element I added to the game and it's a bit of a mess, so you're not alone in finding it hard to understand, there's quite a few weapon stats listed that aren't all that important compared to 'damage' and 'cooldown'. I was in full 'just get it working' mode by that point :)
It looks like Itch double-posted your comment (it's been doing that to me a lot too) so I deleted the duplicate. :)