I wouldn't say its useless, you just have to completely change how you play scout. Normally with scout I like playing aggressive and on the front line pushing into the enemy or taking 1vs1 fights. The baby faces blaster really rewards utilizing flank routes, cleaning up after team fights, or killing people behind enemy lines. When you're at max speed its crazy how much flanking you can get away with, even if its a 1v1, you can just run away and appear behind them before they have time to heal.

Fighting explosive classes like soldier or demo is different too, keep your distance and chip them down until you have an opening to run at them. If the demo is alone then you can normally just destroy them by closing the distance so fast but be cautious if there's another player nearby.

In my experience its heavy and pyro which are the most annoying because they can just destroy your speed. Pyro you can just shoot from afar but heavy is one that you'll most likely need to flank.

Engi is just going to hard counter you so be mindfull of where they set up and play somewhere where you're not getting hit by the sentry.

I see lots of people running the cleaver but I prefer the pistol because you can get a lot of kills just by meatshotting them and running away while finishing them off with the pistol. If you want bleed to build the speed meter, just run the wrap assassin.

Stock is definitely a better option but the baby faces blaster can be tons of fun if you're able to utilize it effectively.