Thanks for giving it a try! Honestly didn't even think about the slime doing loops when making it, but it's certainly on theme. Everything happens at roughly the same time, so the AoE should happen every 5 seconds- that slime brain doesn't seem to be very smart, always with the same answers to everything.
I completely agree with it not being very fun when trying to use the least knights possible, the little time I could spend playtesting was mostly about seeing how well the game worked while brute forcing it.
The extra classes and attacks you mentioned could be a really nice addition to a more strategic version of this, but if I were to continue this prototype, I think I'd like to continue trying to make it about rushing the boss with hundreds of knights, would have to figure out how to make the early loops more enjoyable/more impactful(?) while making spawning knights quicker somehow (maybe completing certain objectives duplicating certain loops, just offsetting their position a little for extra coverage).
Just a personal opinion, but I think rating artwork in a gamejam should be more about how stuff fits together and looks rather than if the art is original or not- not like I'd rate this any higher, I was extremely close to using an MS Paint green circle before finding that slime. Honestly if I hadn't found the slime sprite I would've probably not released anything at all, didn't even know I'd release it 4 hours before I did.