The QF is almost certainly at least as effective as regular uber.
Why is that a problem exactly? All our talk about making the game faster, and the solution is literally handed to us in the form of the Quick Fix. Remember how we said the two ways to increase a skill ceiling is by making aiming more important or by adding advanced movement techniques? Quick Fix.
I fully expect to see the QF and Kritzkrieg become the mediguns of choice for competitive medics. Not because the Quick Fix is more powerful, but because it's more FUN. It is way more exciting to be constantly aggressive and flying all over the map than it is to stalemate out 9 times a game and wait for uber to build. And if everyone is using the Quick Fix, that makes full time Kritz viable. I'm not saying it's a counter to QF, but it's certainly equal to it. And Kritz is fun too. The Quick Fix by proxy is responsible for those absurd DPM numbers that have popped up in the last week or two.
You can still run Uber, you just get to be boring about it. You get to play with HRG level of passiveness, not committing to any fights until you have uber because you aren't capable of playing as aggressively as the QF team. Or much more interestingly, the meta might simply invert itself, and we'll have suprise ubers for pushing last instead of surprise Kritzkriegs. Uber will always be best for pushing into an entrenched team.
If the Quick Fix does become more effective than uber it will be because the weapon has a higher skill ceiling, not because it's inherently overpowered. And that's a good thing, an amazing thing. Quick Fix makes TF2 more advanced both on a player level and a team one. It might make Uber obsolete, but there is so much to gain compared to what would be lost.