Thanks for playing!
I tried my best to balance the boss fight so that it worked in the way you experienced - taking the time to fill out the tree should have had a reasonable reward, and I felt like significantly speeding up the boss fight was a fair enough return for the time investment.
Enemies were something I was a little concerned about honestly. I didn't want to try to shoot for the moon with this jam, so that required really just having some basic enemy types, and the shield enemies were on the cutting room floor for a bit. Their entire purpose was to make the other enemies more difficult by just being a wall, letting other allies attack. I think one of the things that helped was changing the aggro mechanics during the grace period, since previously enemies would just stand around, until hit. But now, if there's a group, they'll all come after you, which forces you to handle the shielders so that you can take out the actual threats. Small change but I do think it made a big difference.
On the topic of end game runs, I've heard something similar from teammates, so I'm going to look into enhancing the spawn system to start spawning enemies once the time reaches halfway down, and I'm hoping that will help offset the map feeling empty once you get far enough in a run.
Thanks for the feedback, for taking the time to play, and I'm glad you enjoyed the game!