It can be overwhelming if the newcomer worries on how many movelist there is (it isn't as much compare to Tekken), knowing which move to counter, & some characters are either ones you don't find yourself doing pretty well (maybe something like Bass, Gen Fu, Bayman to name a few) or inputs that are not easy to pull off (example the Izuna Drop). Even if DOA can overwhelm players at first, there are always characters that are much more easy to use or pick up play without training yourself.
TBH, I find knowing how to use the defensive moves (other than block) to be a good bit of the problem. You don't NEED to know the whole moveset of a character to do well, as long as you know how not to get beat by the other character. Knowing how to punish someone after blocking them, knowing how to sidestep, and, the worst but most effective, knowing when to hold and which hold to use. To do these options, you need to know the whole cast almost as if you main them. Oh, and don't get me started on stagger escape.
Honestly, Street Fighter will always be in every tournaments (with few exceptions or until olds get replaced eventually) even the lineup will always show SF as number one along with Ultimate Marvel vs Capcom 3 taking number two and any SSB title will get the number 3 spot (there might even be more than one game, even one that was not officially made by Nintendo Project M, despite it is a modified version of Brawl to play like Melee) although despite SSB Wii U is at number 3 in EVO15, SSBM that was originally number 3 from previous years ended up on number 8.
And this is no surprise.
But anyway SSB for certain is indeed easier to play (if you were to ignore part of Melee's tech, speed, & combos) & learn character moves or how to play the game, which pretty much any players (unless they don't care about SSB) will likely pick up a copy of SSB whether they'll play it just for fun or for competitive play.
And immediately you see the pattern. It's easiest to play, but is balanced so that there's actually a game there. Thus, you an expect it to be the most played.
Street Fighter is a little easy (with some exceptions to many mechanics or how it is use), but it would still require to understand on how the special moves or supers work if that newcomer has never played SF or other 2D fighters, even if they did played 2D fighters they've never been able to do d,df,f input for example (which 3D fighters have inputs like that too). Some moves, newcomers will not easily execute or be able to pull off during matches (like 360-degree type inputs from either Zangief, Honda, or T. Hawk to name a few, or Delta motion for supers from Guile, Vega/Balrog (Claws), or Decapre) which part of these inputs time & bit of practice. SF can only be easy if newcomers can do inputs that doesn't require too much to learn like Ryu, Guile (except Supers), or Chun-Li for example.
And we see it again. And it gets more fun, when you see which characters are used the most. The Ryu like characters (Ryu, Ken, Sakura) get played alot. Next tier you get the Guile type characters (Guile, Boxer, Honda), then you get the really obscure characters, then last you end up with Gen.
Part of getting into fighters will still apply to the newcomer or players themselves what they prefer for games or how much they understand games (even if they don't have much skill). People could still want to play games that despite it isn't easy, would want to beat it or learn them (maybe similar on how I got into fighters). Part of 3D fighters is that they've expand more when it comes to mechanics or combos for example, even if it meant that these added mechanics or heavy combos just divide opinions on what they prefer. Even SC series started to become much more simple, even Tekken 7 may try to appeal beginners which some people will not be a fan of. The choices to offer is very limited since there are 4 main title to choose (not counting other third party media games), there are other 3D fighters that didn't see more titles or certain series stop at recent tile that did no justice to the original.
Personally, i think the secret isn't simplifying the game itself, so much as getting the game to a winnable level from which you can expand on, to get people to play it well. When you first start playing smash bros, you don't immediately learn how to shield or even roll dodge. These are things you learn after you master the rest of the tech in the game, despite it being really simple. You don't need those to win, but it helps alot. The idea is, you gotta have fun before you're going to invest deeper into the game, so you gotta try to get people to that fun stage as quickly as possible for the game to succeed. Hopefully, you can get them there without them learning that mashing is how you win.