Blue Flare might be weaker than V-Create but 1. it doesn't lower your stats (which leads to Victini to be forced out, which is bad for a pokemon so vulnerable to Pursuit and entry hazards), 2. Victini's checks tend to have higher defense than special defense so the damage output would be similiar.
Blue Flare is a very worthwhile move and I can easily see a special set outperforming the physical one given that your opponent expects the latter.
1) Victini's theoretical gamble is thus: if sun is up and anything offensive switches in, it dies. Period. Most defensive Pokemon, like Hippowdon or Gastrodon, will not outpace him even at -1, so he can go for the 2HKO. Tyranitar is the only Pursuit mon that's even trying to mess with Victini, but a non-Choice set can easily go for the OHKO with Brick Break; CBTar is still slower at -1 and TankTar is slower at -2.
#2 is completely wrong. Tyranitar, Latios, Latias; we're already at three common Victini checks that take Blue Flare with no problems whatsoever. Then we can add Gastrodon, and Pokemon with equal defenses such as Rotom-W and Starmie where Blue Flare is just a weaker move. I'm going off the top of my head and that's already too many. Using a special set also leaves you walled by Chansey and Blissey, whereas a physical set is walled by nothing.
The whopping 50 BP difference eclipses any kind of Def/SpDef disparity his switch-ins may have. If you sit down and do some calcs, you'll notice that raw damage output increases more quickly with BP than raw stats. Both have a similar effect on the damage formula (EX: if stat is doubled damage is doubled; if BP is doubled, damage is also doubled), but there is a much wider array of move power differences than than stat differences among OU Pokemon. You'll see move BP double easily among Pokemon (Ice Shard -> Extremespeed) but not stats (Brelooms base 60 = 156; Tentacruel's base 120 = 276).
In short, stronger moves make stronger Pokemon. This is why Victini outdamages everything in OU with V-create,
including Kyurem-B, and why special Victini won't be viable in OU even with a slightly stronger Fire Blast.
