True, fila-mints would be an offensive choice, reinforcement a defensive (duh!) one but also a mix of offensive/defensive if you are using pea-nuts, etc.
Plus, mints are supposed to be a reward for players that fight hard in Battlez, something that makes higher league more competitive (I don't see how it could be interesting to spend a lot in gems for gauntlets to get to the top positions every week if at the end of the week you used more gems than you won with rewards + daily ads/quests).
So what is the point to get a reward which is, so far, kinda useless for Adventure mode and totally useless for Battlez mode ?
Yes some level are really difficult and are no fun at all. Especially the ones with thoses sneaky and annoying chickens or weasels. Or the ones where you have to defend some plants and a random parrot steal it out of nowhere. It should be call Plant vs Animals and Zombies at some point x)
For Western Zomboss, use power snow to directly damage Zomboss, while using your plants, it will help.
If you wanna finish Adventure mode I would suggest Larry Tseng or Plant vs. Zombie Gameplay Youtube channels. They are doing good walkthroughs with lvl 1 plants, no prem, etc. But even with thoses, it is sometimes really tricky to finish some levels if you are not doing it at the exact same time or if zombies are coming from another spot, etc