#19 is exactly right, but I actually think all three of those classes could be nice if they were implemented better.
if airblast actually had a reasonably sized hitbox (instead of just being a giant disk that pushes you straight up no matter how it makes contact with you, nor your previous momentum) and functioned more like rocket knockback i think reflects would be a really cool mechanic that would allow for clutch plays. reflect jumping is sick too.
i actually even think you could make a similar argument for engineer. this ones a little harder to think up a 'fix' for, but i think if there were more things to build/ more options the capacity to out-think your opponent might be cool. atm the only really 'interesting' things i see people do with engi are sentry-jumping and tele-fragging: i'd personally love to see a building pda unlock for both of those, making either one easier/ more viable.
as for heavy, i think if you tightened the spread cone/ otherwise nerfed the class to be less of a defensive tank and then gave him some sort of interesting aoe buff to teammates he wouldn't be that bad. idk actually maybe heavy's unsalvageable lol.
nerd essay