It's about damn time I got another video out there.
This one's...bound to be controversial for anyone who still follows Smash 4 competitively.
That was an interesting video.
I'll give my two cents on the topic, just bear in mind I'm not a competitive player, but I do follow other fighters.
I'd say there are two main issues at hand here that skew perception. The first, you said it yourself, but both can be very tough to deal with at low level competitive play. Thus, a lot of players start to feel that the MU is incredibly unfair, and it's very noticeable whenever you play against Bayo, even after the nerfs, her aerial game is RIDICULOUSLY strong, in most cases, you're better off not even trying to engage her in the air, and just trying to bait and punish, which can make the fight incredibly tedious.
Which brings me to my second point, and this is the core of it all.
Smash 4 was not built to be a competitive fighter.
You can't use the top players as a measuring stick for what's broken and what's not. Just cause there are ways around certain tactics, doesn't mean those tactics can't be overpowered. The result winds up being that low level competition, simply isn't fun, and this is the outcome of trying to play a game that wasn't built for competition, competitively.
Contrasted to other fighters, they can be a lot of fun at ALL levels of play, because the games are designed and balanced around competition. The top tier isn't the measuring stick for the rest of the scene, and these games often have built in mechanics to make certain things that might FEEL OP, less frustrating. One example being combo bursts. This the Achilles heel of Smash 4, and combined with the emphasized focus on defensive play, a lot of matches start to become more tedious and boring, as there are a very limited way to deal with certain situations. Games require options in order to be fun, different players prefer different playstyles. However, Smash 4 seems to funnel itself into there only being ONE way to play in order to be competitive. Only ONE way to deal with certain MUs, and it's this lack of player expression that frustrates people, and has them find an outlet through which to vent their frustrations on, that outlet being the two characters who seem to have the most ease at low level play, which.... is where most of the scene will find itself in any game, as competition by nature creates a sort of pyramid structure.
When a large chunk of your competitive scene isn't having fun with a game, the answer shouldn't be to point at the highest tier as an example of how the game should be played, it should be to carefully look at what's causing this stir of emotion in people.
And sadly, in the case of Smash 4, that seems to be the lack of competitive focus when designing the game.