Personally, after a short while I didn't feel the battle system came across as pointless or an afterthought. It's hard to see how you can reason that when the entire game world is built around it, and the economy of the stickers and locations of enemies is part of the ecosystem.
It seems you'd almost have to purposefully try to not play the game right and run through it to miss that.
To be frank I wasn't sure myself if it was going to work out initially, like to the final level in world 1. By that point though, and especially with the new enemies showing up in world 2, it became clear that the trash stickers in the environment were inadequate and you needed to start fighting to bankroll coins and make proper use of your inventory slots. For an efficient combination of stickers.
It doesn't hurt that the battles are fun, don't take too long when you know what you're doing. In addition, they remain interesting because of the very fact that you don't have a default "free" attack like a basic stomp and hammer attack. By making every single action cost a sticker, there's no motivation to be lazy and just mash basic attacks knowing that you can survive attrition to your own HP by the time the enemies are dead. That is in fact a big problem with a lot of traditional RPG battle systems - high level strategy breaks down and becomes a bit pointless when you can just perform mindless actions and outlast the enemy because say, you're wearing good gear or have overleveled hit points. That doesn't happen here, so far at least.
To a degree, I'm reminded of the junction system in FFVIII - where every spell cast cost you stats, and made you think about what you were spending.