WOW is basically DAD which Midevil, kind of stuff. Darkness, secret powers, Metal and stuff. Stuff from Ireland, Scottland, and England. During the introduction of RPG games from the west to the east, many Japanese programmers, and artists decided to make there own variation of games........This was back in the mid 1970's during the Microcomputer boom!!!
Basically most videogames from Japan that is adventure is really RPG games. In the case of Mario and Sonic type games. Even shooters are RPG's.
In the west, including China, and Korea. Many adventures games lead you in exploring a haunted house, or something like that. Being able to interact with objects.
Paper Mario on the N64 is basically the unofficial sequel to Mario RPG on the SNES. Since Sqaure owned a license on all the non-nintendo characters, they had to reshape it into there own. Super Paper Mario is again an RPG but in the case of an adventure game.
So to answer your questions, in comparison to Zelda, Soul Revear, WOW, PSO this is not an RPG game. However in japan a game like WOW, is no diffent then Mario.
There is no differnce between, all three mario games. Since they all fall under the RPG that is from Japan. There has been various of other Adventures games in the west that does the same exact thing.
Imagine if you could strip a board game down to it's bare bones, and make everything as simple as possible. That is how you should conisder these adventure games RPG's. It does not mean your going to like them, or you need to play them. Like how I prefer Wario over Mario. Or Bomberman over Megaman. You do not need to play every single RPG/Adventure game out there.
There is no difference between all Mario games like the ones you mentioned. Asides that Paper Mario is a direct sequel from Mario RPG and has attributes.