The chapter system of Mother 3 makes it the least aimless of the entire Mother series. :/ I really don't get that. I honestly feel that anyone that likes Undertale but dislikes the Mother series is a rarity. There's definitely a lot of good overlap between the two IPs.
I think it's certainly possible. If you don't like the rpg aspects of the mother series, there is very little chance you'll be able to enjoy the games. Not that there aren't a ton of other things to enjoy about the games, but if the fundamental RPG loop doesn't grab you it would be a real slog to make it through. There's still a lot of gameplay in those games.
Undertale skirts that by being very rpg-lite. There's something like maybe 12 pieces of equipment in the whole game? Limited enemy types, and depending on how you play there are certain rpg aspects of the game you don't have to engage with at all. It plays on RPG tropes and you'll get more out of it if you have played and enjoyed rpgs (particularly snes-era ones,) but the actual rpg gameplay is super thin. You can beat Undertale in the 10 hours it takes to decide you're not really feeling a typical rpg.