IDK I think the metagame revolving around a character is dependent on the community, it's not a matter of being dumb as an okay thing, it's a matter of how the community is going to approach it.
And disappointingly, their method is to just switch to him :/. I don't know what it is (I imagine players just want results) but that's what happens with Smash, but you don't see it a lot in games like ST as much, even with their obvious dominant characters like Dhalsim, Claw, Balrog....
The roster balance in Smash 4 promotes more diversity than ever before but how many people are utilizing it is the real question. (Low tiers not TOTALLY unviable but still not good ofc, the balance isn't PERFECt or anything but there's a lot of good characters that aren't Diddy that CAN compete and fight him.)
Because there's money involved.
Let's say you (you being ANYPERSON, not you yourself) hypothetically just spent 100 dollars in entering a tournament, but if you win it you'll get 1000 dollars instead!
Would you use a sloppy character like Zelda that is hard to use, requires precision, incredible reads and has a ton of weaknesses, even if she's "viable," or Bowser, who's ridic strong but can become a piñata against certain characters, or Villager, who will really feel the pressure from the predominant faster characters?
Or you could use the objectively best character in the game. And learn him. And use his ton of advantages and basic lack of disadvantages.
I mean, I'm not being like "THAT'S THE OBVIOUS THING TO DO" cause I never really play top tiers (for whatever reason), it's just that it's the most pragmatic thing to do if you're actually making money off playing Smash. Of course there are players like Nairo and Nakat who use other characters and all that ****, but that's the reason top tiers are so predominant. Have you ever seen tourney matches for MvC3? Everyone uses the same party because of the same reason. Using, like, say, Zelda in a tourney where there's money involved is like not tuning your car before a big race. It might be because of preference, might be because of style, as the sisters put it, might be because she's your best character, but she's still a car that's not properly tuned. And you're racing against like ****ing Subaru ralley cars out there.
I'm not trying to be patronizing, it is just really the reason behind it.