Lock scouts at 1 per team and make every scout use a shortstop
In all seriousness though, there are a lot of ways but the thing to keep in mind is how the nerf would play out in different skill levels and how it will affect the skill floor, the ability for a new player to crawl in and get started. I am not a good scout, so just keep in mind these are just my random, low-skilled thoughts. Lowering Scout's max health might not seem like a big nerf if you're a higher level player who has pretty good movement, but for new scouts it will simply kneecap them, and scout in pubs will become virtually extinct. This would raise the skill floor, requiring new players to do a chin-up just to get in the room (metaphorically speaking).
In contrast, reverting the medigun speed boost will not raise the skill floor or lower the skill ceiling for the scout, it would simply reduce the ability for a Medic to flee from every danger.
You can take the momentum stopper off his scattergun but now you've lost the meta's best anti bomb class, unless you can expect your soldiers to hit every airshot (oh, and now Medic can't run away from the bomb as fast as before since we've agreed to remove the speed buff). Adding with damage falloff, the Scout can't do much damage to a high bomb soldier, therefore a scout would need to wait for a Soldier to land or get close to the ground to take them on. If you've ever faced a Soldier who can sync their rockets during a mid bomb, you know this is actually quite frustrating to fight (to me at least).
I suppose you could add a new way to hinder bombs without needing to hit every rocket, perhaps an airsticky buff or a new hitscan weapon like a railgun (not necessarily for the scout) (or pistol buff?!).
I wonder what would happen if you had to reload a clip instead of individual shots, with a longer reload time, taking you out of the fight for a second if you've exhausted your ammo. This would not change the amount of damage you can do from the start, leaving new Scouts the same capabilities to do damage as they have now, but they (and higher level scouts) would have lower dpm over longer fights, and they wouldn't be able to get away with missing 10 shots.