I do think what the OP might meaning is less about "can this game be played competitively?" and more "will this game be played competitively for a long time?"
I honestly can't say. While I love the changes done in this game, I also feel like they didn't go far enough in terms of changing things up on the high-level end. I think this question stems from the ever looming thought that Melee will be the only long running Smash title solely off of its competitive basis, which MIGHT seem that way, unless Sakurai does do what he said and revamps the series in the next entry, in which case Smash 6 and Ultimate could be as different to each other as Ultimate and Melee are.
But I think we are looking at this in the wrong way by trying to look at specifics in the games themselves rather than how players interact as a whole. This balloon knockback talk that I've been seeing in this thread lately is honestly not worth talking about, because it's clearly established that that mechanic is meant to decrease downtime during the periods neither player can directly interact, so high level player interaction is, in theory, not affected by it at all.
Now are we going to talk about why Melee has lasted so long as a competitive force in fighting games and how Ultimate fairs? Well to compare the two, Melee has more overall options the players can do during the match. However, due to Ultimate's slightly slower overall pace and easier to read animations, I would go as far as saying that Ultimate is the better game in terms of spectatorship, which, believe it or not, is MORE important than competitive depth in terms of longevity of a game.
However, this only appeals to the casual and semi-casual masses, which means the core playerbase of Ultimate MIGHT become less robust than Melee's in the long run. What ends up mattering is the potential for how these spectators end up seeing the game and playing the game itself. Luckily, Smash Bros is an easy to pick up series, and Ultimate wins over Melee in that regard as well due to easier to intuit controls and techniques.
Even though it sounds like this is all in Ultimate's favor, that last part of player options creeps in again. Options matter to a core fanbase, and is what can give a game breadth and depth all in one. Ultimate, compared to Melee, gives far fewer potential options for player interaction, though nowhere near as bad as Brawl or Smash 4.
As a summary, Ultimate wins over Melee in terms of general spectatorship and ease of entry, but Melee wins heavily in building a core fanbase. It's because of these that I can conclude that Melee will still win out in longevity over Ultimate in the end, but will still wane in popularity as the non-core fans continue to leave, and the lack of easy entry means the numbers may not grow as strong as they could if Melee had Ultimate's positive traits.
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Personal opinion is that I like Ultimate and am personally conflicted towards Melee, mostly because, as a budding game designer, Melee is BEGGING to be revamped into a proper spectator esport that is properly "easy to learn, hard to master" instead of the current "easy to pick up, hard to learn and master". And the overall success of Melee kinda infuriates me in a different sense; the more time it is not dethroned as the definitive competitive Smash Bros game, the more stuck we become as Melee eventually atrophies and nothing else is there to replace it.
In addition, we also get more and more hardcore fans who turn their nose against anything not resembling Melee, even if those changes are improvements to the overall experience. I've already been getting this vibe across the forums here and on reddit. People wanting DACUS back even though you could just add the much better proper wavedash and be done with it, people who think the pinnacle of skill involves either the amount of buttons needed to do a singular maneuver or how difficult it is to pull it off at all rather than how you USE those maneuvers to win, people not wanting nerfs but for everyone to be buffed to S tier levels, even though most likely S tiers are S tiers because they are imbalanced compared to not only the other characters, but against the median the game itself seems to be designed around.
These are personal gripes that mean little to this discussion, mind you, so you can ignore this second part if you wish.
. He was the only character that played like that. Even with the unbalanced mess Melee is you have like 7-8 characters you can choose from. Brawl was 
