BTW, I know there were some concerns (and some concern trolling XD) earlier that you wouldn't know how much damage your attacks do because no damage numbers are given. As a moderate alleviation of that concern, I think it's worth noting that when you attack enemies they lose color from the bottom up, depending on how damaged they are, and when they're nearly defeated they're almost devoid of color and the top of their body curls forward.
While this doesn't give an amazing idea of how much damage each hit does, it does show you how close the enemy is to defeat, which is at least as useful and IIRC not present at least from the get-go in any Paper Mario or Mario & Luigi game (I think badges might give similar functionality).
FWIW, though, since non-boss enemies almost never give the player a very hard time in the Paper Mario or Mario & Luigi games, seeing how close an enemy is to defeat is at least as useful as seeing how much damage you've done to them. It's also pretty evident which attacks are stronger or weaker than others based on the aesthetics of the card.
In the prior Mario RPGs (excepting SMRPG, which I can't speak to since I haven't played it), you know which gear and moves are more potent due to numbers given, but apart from "this thing is stronger than (or provides more defense than, raises speed compared to, etc.) that thing," it's not as though serious number crunching was generally necessary.
So in this game there is no permanent gear to equip that I've come across, but, purely on a combat side though there is definitively less depth, it's not as lacking as it may have appeared. I personally enjoy it and the enemies' moves and banter is clever, it's interesting to be able to summon enemies from cards, the timing is limited to one button but is often trickier than in at least the Paper Mario games for some of the basic attacks, and I believe it was indicated the Thing attacks have their own timed attack benefits but I'm not sure yet how to find out what they are.
The bottom line, the combat is definitely not as deep as in the other turn-based Mario RPGs, except for Sticker Star, which it is similar to. But, for the most part enemies seem less densely populated in the areas of the game we've encountered so far, so battles if I'm remembering Sticker Star correctly aren't quite as frequent as they were in that game.
The enemy moves and banter, the ability to use enemies as summons (which IIRFC wasn't in Sticker Star), and the benefit of accumulating paint HP essentially, makes battles have a bit more depth to them than in Sticker Star. But if you disliked Sticker Star, take my musings with a grain of salt because I liked Sticker Star a lot.
BTW, I know there's been a bit of debate over whether there is any purpose to increasing your paint meter. It's really going to depend on how you play the game, I think. If you get into most battles you encounter and are trying to paint all the areas, while paint in the areas is (cumulatively) somewhat plentiful, it helps immensely to increase your paint meter. We frequently are running out of one kind of paint or another (often one sort of paint is not as plentiful in an area that features a color scheme primarily based on the other colors) and will have some battle cards half-painted. In one area we ran out of yellow paint and weren't able to paint some of the spots we saw until we came back. One type of enemy takes a surprising chunk of your paint reserves of one color away and many of the environmental suppliers of paint (trees, flowers) only give you small bits of paint at a time. If you're exploring every nook and cranny and painting, it's significantly beneficial to be increasing the paint meter.
