I completed SMRPG for the first time a couple days ago. Fairly unique experience; I used some codes to make it so I could play as Bowser, Geno and Mallow after Booster's tower, so no Mario and no Peach. Those two characters, especially Peach, make the game far too easy.
Apparently the general consensus is Bowser is the worst next to Mallow, is that really true? In my experience, Bowser was by far the best of this trio as both the tank and primary damage dealer when Geno Boost was available. The worst party member is easily Mallow. His terrible attack damage and awkward magic that has bad/non-existent healing compared to Peach means he's usually the one reserved to heal or throw the Pick Me Up.
A lot of the time fights just revolve around the inventory limit and Pick Me Ups. It's an odd sort of balance. You basically have infinite money but all you need is Pick Me Ups and the occasional mushroom the entire game.
Geno himself is so weak defensively, he was commonly the first to go down in fights. He has absolutely awful magic defence. Keeping in mind I did level up only his power, guess that might've been part of it, but at least Mallow has high magic defence going full magic, far more relevant than high defence in this game. Bowser had such naturally high HP he could tank magic for the most part when I went all into his power on level up.
I can see why Geno might've caught on as the star of this game just from the very imbalanced party choices. Geno is the obvious back up to Mario compared to Bowser, whose spells suck, and Mallow, who is easily the worst party member in the game. Geno has a fairly decent selection of spells too and as Peach is broken, it's obviously going to be Mario/Peach/Geno or Mario/Peach/Bowser. I just find that is very, very easy and broken. The challenge that Bowser/Geno/Mallow presented made the game a lot more palatable.
As a character Geno has the third most lines after Bowser and Mallow. Funnily enough Peach has almost no lines in the entire game? At best she's below many of the important bosses. Booster's obviously got more lines, it's just funny when she's not in the party my whole game how she seems totally irrelevant. That doesn't mean Geno gets to do a whole lot though, it's obvious he's the pick for this game because he's clearly the easiest character to translate to Smash. Good luck promoting Mallow's power set of random lightning spells, a rod and giant hands.
I also went back and defeated Culex after I beat Smithy. The whole game was pretty easy even doing my mod and Culex was a massive step up from the rest. I ended up just giving myself the lazy shell and egg via codes which breaks the game. Culex is a really badly designed super boss that relies entirely on RNG for his crystals and I was happy to cheese him down. Smithy on the other hand, as well as Booster, Dodo/Valentina and many of the weapons were both good boss fights and great characters. It's just lame how Peach's healing, Mario's spells and these items break the game.
After all that and going through the game I'm definitely a fan. So long as we get K. Rool I wouldn't be against Geno if only to get some SMRPG content.