I just don't see Hero's RNG elements being enough to trounce skillful play.
All of his RNG elements can be avoided by the opponent. Even his "one hit KO" options are very easy to see coming. It's not like has an automatic "I Win" button he can press that just kills his opponent without them being able to do anything to avoid the situation.
I cannot imagine a scenario where a Hero player of inferior skill comes in, goes through pools and wins sets carried by RNG, goes up the ladder, and ultimately causes upsets in a tournament due to getting "lucky" with Thwack, a side smash crit, and happens to be blessed with magic bomb during a ledge guard.
Yes, these things happen, but a better player is going to lose a stock, come back, and continue destroying them anyways. Actually, a better player is less likely to be put into disadvantage against Hero as frequently, is less likely to open themself up to be hit by a side smash as frequently, and is less likely to, in general, grant windows of opportunity for Hero to roll some dice and get lucky with crits or menu options.
Across the entire duration of a full set of games, I just don't see that level of RNG happening.
Many people are also forgetting many other sources of "RNG" that are present at many levels of play, including the ultra-competitive, for all Smash characters. Two framing ledges, for example. Even at the highest levels of play, players do not regularly succeed with two-framing attempts. Missed techs, especially up against the underside of a stage. Many top tier players fail these all the time. They'll try, and ultimately have a rather low success rate when it really counts. These two things could be considered "RNG where skill improves your odds." A better player may perform a life saving tech 60% of the time, whereas a poor player may do it 5% of the time. Either way, there is some luck still involved here, and that's for all of Smash. The timing windows are too precise for even the best player to succeed at a 100% rate, so you try your best, attempt the input, and hope your insufficiently precise timing happens to land on the window it needs to be to see the desired outcome. Yes, this is "Luck," and it's everywhere. A better player will also avoid situations where they would need to perform a life saving tech more frequently, as they're less likely to be in disadvantage off-stage against a poorer player in the first place.
Another example is reads after tech chases. You think you have a good read on what your opponent may do. You prepare for them to choose that option. They seem to favor rolling away from you after failed techs. You kill them because they did it again, but what if they decided to get up attack? You can never be totally sure what your opponent may do, and, to some extent, trying to read an opponents options and punish them for it is a level of RNG due to uncertainty. The ultimate deciding factor in your success here is outside of your control, no matter how strong a read you think you have. You need to get "lucky," Hero or no Hero.
I've fought a ton of Heros so far online, and it does not feel unfair. Sure, an occasional Thwack killing you at 30 can be rage-inducing, but it isn't determining the overall victor across a string of stocks, matches, or sets.
People who are stating Hero needs to be banned are way over-reacting to this entire situation and need to look at the game overall and realize there is already a lot of RNG in Smash.