Yeah, you can get 100k+ kills having fun, but if you want 1million+ you've gotta do the same cheese-dick item farming everyone else does.
The game needs more ladders:
Character Ladders
Speedrun Ladders
Achievement Ladders
My highest from a few days ago was 133k with Noelle before I quit. If I could see where I placed on the Noelle ladder specifically I'd bet money I would've been top 5. Why? Because she sucks ass. But I want to see people push "bad" characters more than I want to see everyone spam Bandit because he's meta.
They also do need to make the option to just infinitely go through stages and defeat harder mobs and bigger bosses. Even then with it's current state you'll probably be insta gibbing everything in stage 2 or 3 and run through everything until you're eventually one-shot by a goblin swarm after you run out of Zarwarudos.
And at this stage they definitely need to be able to toggle off skill effects. I've seen people with 1million+ kills die on the boss because they literally can't see the ground SEVERAL times.
It's got a lot of room to grow, but yeah, that climb through unlocks and your first time getting 100k is a 10/10 game experience. After that it's seed/RNG farming to set up a run and it's more like 5/10 gambling experience.