Super glad you played through it and got to the boss! Also very valuable feedback, thank you!
I agree with the mining currently feeling a bit underwhelming. We should add more mining multipliers in the skill tree.
Regarding the chest, we were actually planning to make the chest AND mining be "real time" events where the invincibility bar would continuously go down. This would incentivize the player to perform them faster so they use less invincibility. This is definitely something we will implement in a future update.
We hadn't thought about utilizing the side mouse buttons, that is a great suggestion.
Thanks again for the great feedback! Going to try your game soon. Look out for feedback from my partner const0 since my itch io is getting restricted commenting.