On one hand, I object to the banning of V-create as a matter of setting a precedent we can't possibly mean to keep up. In the same vein, we could retain Staraptor without Reckless, Crawdaunt without Adapatability, Zygarde without Dragon Dance or Coil, etc. Furthermore, it opens up the possibility of further tier manipulations, like taking existing Pokemon and making them stronger or weaker to fit some sort of viability mean that all pokemon fall into to have a truly "balanced" metagame.
Of course, it doesn't necessarily lead to this, it only creates precedent that makes it harder to argue against these ideas in the future.
There is also the issue of inconsistency - a series of complex requirements to use certain pokemon will confuse someone new to the tier. This, one could argue, is analogous to when Shadow Tag was banned - Gothitelle was still usable, but not the way it was in OU! However, this is a false conflation, as Gothitelle was practically unviable in the tier, and the purpose of the shadow tag ban wasn't to make it viable, merely to remove the offending playstyle.
I think that banning V-create is really just not worth it for the precedent it sets. Getting to use a V-createless Victini is nice, but it would signify a shift from banning to make the tier more balanced to nerfing to make the tier more balanced, and that's a shift I don't think will pan out well in the long run. What if our nerfs to Victini cripple it so much that it goes down below 3.41% usage and into RU? Are they meant to retain the V-create ban and further add a "Blue Flare" ban in order to retain Delphox's niche? It just seems a bit silly.
Addressing points:
I can see where you're getting at with the complex bans to keep things in UU, which I agree is absolutely stupid. However, Victini stands out differently as the sole user of V-Create currently in the tier.
Going back to your examples stated in the first paragraph, every single one of these Pokemon are because they are broken in their own character. By character, I mean that their typing, stats, and/or abilities in conjunction with their moves make them broken. There are a number of Pokemon that carry Reckless, such as Hitmonlee and Mienshao. What makes Staraptor toxic is its Brave Bird, speed tier, and Base 120 attack.
Essentially, the question becomes this: Is (ability/move) broken on the majority of Pokemon that have it? If the answer is no, then the Pokemon itself is inherently broken. IF the answer is yes, then we have a completely different issue altogether.
A good example of this would be the Gen V Sand Veil/Snow Cloak ban. As long as you could maintain and win the weather war, every Pokemon that had Sand Veil had an uncompetitive advantage over the opponent. Likewise, Shadow Tag is also pretty much broken on every single Pokemon that have it. Let's be honest here, when Goth was OU, we all had the great idea to use Gothorita with humongous success. Hell, even shit like Wynaut can be useful to fill a similar niche Wobuffet would have held if that thing was still UU.
Addressing V-Create, the move is broken on 100% of the Pokemon that have it in UU (Victini hur durr and Smeargle doesn't count), therefore it's not an inherent Victini problem (100s across the board, Fire/Psychic psh). The problem comes from the cancerous Base 180 Power that makes it ridiculously hard to handle. So no, it's technically still banning broken aspects of the game and not just nerfing and tweaking Pokemon.
Finally, I'm not quite getting where you were going with the "Ban Blue Flare" example. First off, Victini's Blue Flare is comparatively similar to Delphox's Fire Blast in power output:
252 SpA Choice Specs Victini Blue Flare vs. 252 HP / 252+ SpD Eviolite Porygon2: 132-156 (35.2 - 41.7%) -- guaranteed 3HKO
252 SpA Choice Specs Delphox Fire Blast vs. 252 HP / 252+ SpD Eviolite Porygon2: 123-145 (32.8 - 38.7%) -- 99.5% chance to 3HKO
Essentially, Delphox is faster and Victini is bulkier. No one is trying to beat out anyone's niche. Besides, your point about retaining Delphox's niche is highly irrelevant. the Smogon hivemind bans things that are broken, not things that are usurping others niches. UU didn't ban Victini because it minimizes Darmanitan's niche. It's almost similar to saying that we should ban Darmanitan because it minimizes Arcanine's niche as a hard-hitting Flare Blitz attacker.