I love the concept. Definitely want to see more of it in the future. I do have one critique though, the mob giblets just pile up around the arena and I end up wading through them.
A suggestion for how to address this would be to either let the weapon collide with them or make it launch them in the direction the player aims. That gives the player a way to sweep them in a deliberate direction. Then to give the player a reason to do so add powerups or an objective off the platform.
For balance you might then need to either reduce the number of giblets per mob, or require multiple giblets (total or in a time period) to expand the platform. Personally I think the second option because confetti is fun. Bonus points for using weapon knockback to launch mobs at the edge of the platform and having them pop like piñata to expand the platform faster.