Speaking of finishing maps in 2 seconds—it seems to me that having the number of maps be the thing that determines the run length could be sort of limiting to your design choices in powerups. Enough kaboom and the run will just blow through the screens in an instant, and your run will be over before you can fully enjoy in your overpowered nature.

It could be interesting if time was a component to the whole thing instead. Look at Risk of Rain for inspiration, the game gets harder as time goes by. You have a finite number of power-ups that you can unlock per map, so the player is incentivized to try and keep progressing through the maps at a good rate.

In your case, maybe the player could “buy” a +1 map bonus for their run using coins. The cost in coins could be influenced by the current time and the map number. Then, the player will have to choose between strategies that slow them down but get more coins, and strategies that let them smash their way through maps.

It's also worth mentioning that pierce is likely OP to use gamer parlance. It was the perk I would consistently choose over all others, for good reason; nothing else comes close to upgrading from a knife to a bazooka.