I barely used grave busters, wall nut would have been a better option. And yes, I baited necromancers with the methods you just mentioned (I just used a sunflower at the beginning to start with 50sun instead of 100, and didn't use twin at all).
You don't need any upgrade, plant or costume from the shop to beat the full game including hard mode.
The only night level I don't like is level 18, and I'm gonna change it in the next patch.
And although you can criticism the game, if you aren't having fun, you can stop playing anytime you want.