LancerStaff
Smash Hero
Two or three characters who don't gain anything off of customs are the exception, not the norm. They just so happen to be top tier. For just about every other character in the game, you're gimping yourself for not using them. What about when the top tiers get nerfed? And who's to say all of the top players today fully understood their character's customs? I find it likely that they stuck with defaults because they're just more familiar with them.EVO's results today would notably imply that you are not at a disadvantage if you don't use customs.
Instead you're at a disadvantage if you don't use Sheik or Diddy.
The upper end of the event had very few customs-users. Abadango didn't use any customs on Pac-Man, and only one on Wario (Speeding Bike). I know he used Shooting Star Bit, but I can't recall whether or not he used Luma Warp.
ESAM used Thunderwave HSB frequently, but there were several cases in which he opted for default Thundershock (HSB is another of those near-pure upgrades though). However, he didn't win, or even come top-4.
Nairo utilized an alternate blaster for Zamus for extra range against Sheik. Lost the matchup anyway, came in 3rd.
I didn't follow Mr R through the tournament, but I believe he was running default Sheik all the way through. He came in 2nd.
The event was won by a default "double-nerfed" Diddy Kong.
Whether for an attempt to sound neutral (despite the obvious ignorance and dislike of customs from several casters, including D1) or whatever else, the commentators seemed convinced that customs did not, in any identifiable way, cause any sort of upset resulting in an undeserved win by a lesser player. So in essence, you actually don't need to use customs, just like you don't need to use Sheik. But failure to prepare when the ruleset, terms, and sets have been known for months is literally nothing but willful ignorance with a convenient scapegoat.
There's also the problem of the politics of custom sets... They had to be determined long before we fully understood the moves, and we're limited to just ten sets. Kirby I hear has tons of viable sets depending on the matchup... But then his performance is inconsistent because X tournament doesn't let you import sets, but Y does. Stuff like that is all over the place.
And what if defaults becomes more balanced overall then customs? What if it actually is already because low tiers with terrible customs exist?