No.
But Mario Kart is more arcade gameplay and have online play, so casual gamers and not hardcore gamers play a lot more a game like that, than a 3D platformer for 1 user which needs some "dedication".
That is what is happening.

Why? basically a change in gameplay tastes caused by a major broad of audience in videogames than in the past. Many adults play now, and they need some easy and fast games, not a "Banjo Kazooie 100% time dedicated" kind of game. And a serious 3D Mario is usually (apart from 3D World) more like the second (although now, the original Mario 64 is actually a very "arcade-feeling" game, thanks to its simplicity and its fantastic speedruns. In its day, to get 120 stars could take you months).

That's, ironically, also the reason why Animal Crossing had this COLOSSAL success in actual times (online, with huge social interaction, so more women playing it, cause they find that game very cute, and not too stressful, neither a high-speed competitive gameplay game).

In all honesty, there are few terms as pretentious as "hardcore gamer" within video game fandom.

The answer is yes. And it have been that way for a long time. Even when I played N64 I already feel Mario Kart was replacing 2D Mario as the standard "Mario face". The resurgence in popularity of 2D Mario on Wii and DS was surprising, but even then Mario Kart was the winner and now... I think it's just not competition anymore

Multi-player has been by far the most important aspect for a success of a game. I think all most popular games in the world right now have some degree of multi-player. That are of course people who plays solo, I think most of dedicated gaming enthusiasts play solo, mas for majority of people gaming is a more casual and social experience. They want to either cooperate or compete with other plays. That's why I don't think 2D Mario will ever be as popular as Mario Kart

Its a pretty loaded term but hardcore/core vs casual, still pretty accurately reflect different gaming habits. 

Can you make top 8 in any game at EVO?  

Is a poker shark also pretentious? What about a maestro? Or a marksman shooter? How about a sommelier? 

They are different genres, so how can it outclass it? That's like making the claim that Nightmare on Elm Street outclassed E.T. Different things.

I've said this before on here but it MK9 vopied Crash ta racings mechanics with their track design and polish, they'd have the best Lart racer imaginable and definetly overshadow Mario as Nintendos main IP.

Mario Bros franchise is the most iconic thing Nintendo has. Mario Kart is of course a part of the Mario bros franchise.

Comparing the two series: SMB vs MK, well MK is a multiplayer game so pretty naturally it's gonna generally be more popular. It's the most popular and casual multiplayer series Nintendo has so it makes sense it sells more than Mario Bros. But Mario Bros is still the "main" series of games Nintendo has. Also Mario Kart is very similar from game to game, so it's hard to get nearly as excited as a new MK game as people get about a new Mario Bros game.

So while MK outsells Mario Bros, I would not in any way whatsoever say it has "outclassed" Mario Bros.

Mario Bros and Zelda are the two major series for Nintendo. After that comes Smash, MK, Pokemon, and well with how popular Animal Crossing was this gen maybe AC is joining that group as well now.

I dunno about "outclassed" but MK is most definitely the Mario IP I enjoy the most, regardless of how important or iconic MB is. 

I'm not a native English speaker and I see now that the word "outclass" is not exacly what I meant because it can imply "quality". I didn't want to use "popular" because it can be tied to strogly to the sales aspect and I didn't want the discussion to be about sales. Do you have any ideas for a better word? I can change it in the title and in the pool