Sup, Kristin!
Absolutely, once you get high tier items, you can tank enemies easily. Something that would take me time playing to balance and adjust the right progression.
That´s why I gave damage bonus to ultimate defense, to still be useful. I usually test all skills, and the magic resist is quite usefull early-mid. But late game it falls off a bit.
I´ll consider your suggestions when I create a new tab for upgrading towers. Each tower will have a skill tree, and additionally I´ll include some global upgrades like the lives and revive mechanics.
Currently working on a new level and item augmentation system, if everything goes well it will be up this weekend.