Is Pyro more viable? Yes, in certain situations and on certain parts of certain maps.
Is full-time Pyro viable at the highest level? Probably not. Pyro is still slow with short range, meaning there's nothing you can do against kiting, especially since you only have eight to ten airblasts. For that reason, It's also just worse at keeping up with the flow of 6v6 - chasing down targets, rolling forward off of momentum, things like that.
Even though Detonator can put out a lot of damage over time, it does so slowly and doesn't stack well compared to regular spam, since you can't set someone on fire twice, only refresh the cooldown. This shitty spam means that Pyro can't deny chokes like Soldier, and makes pressuring the flank much more difficult to deal with.
Pyro also has to choose between ranged killing power with the Shotgun or spam + out of combat mobility with Detonator / Scorch or Soldier-tier mobility with Jetpack. If it had any two of them it would be full-time viable.
There's also certain points where you're completely useless - long lasts like Granary and Snakewater where nobody is holding close, you don't have the speed to get in, and you can't do anything against Heavies, Sentries, or Manmelter Pyros.
Also a big reason to run Pyro was that he could easily get rid of stickytraps, but since Quickiebomb Demo exists and it's much worse to be stuck on Pyro than to be stuck on QB, that niche is gone.
I also tested Backburner + Jetpack bombing and melting people with glitchy crits, but that's gone now.
It also might be viable if the enemy Soldiers are constantly feeding you rockets to reflect rocket jump off of, but that's unreliable, and I think eventually they will just figure out how to play against Pyro and not let you do that.
I think it's theoretically possible to substitute a Shotgun Pyro for a Scout and do okay, but Scout is just better at doing a Scout's job than a Shotgun Pyro is, and the things airblast and flames bring to the table almost always don't make up for the loss in speed and double jumping.