What we don't know is how buffs are handled with class switching and duration.
For instance if I am an engineer and I hand out a gun upgrade, does it last till death? Now say I buff everyones, including my own, does it stay if I switch to medic? What if I switch guns?
Maybe that is part of the reason why you can't use the higher buff on yourself.
Also as for the hard hitting medic. There aren't many abilities that increase your damage, that aren't buffs. In fact, I'm sure if there are any at all. So a medic hits the same as everyone else, assuming you get the same buffs as them. The biggest difference in hitting power seems to come form different classifications of guns, which is regulated by body size.
So a heavy of any class will hit hard. Arguably an engineer is more likely to be buffed since he can buff himself.
Not to mention that making a Medic/Soldier because the Soldier skills let you hit harder means you have the option of being EITHER the medic, OR the guy who hits harder, not that you get both - class-specific skills will only apply when you're actively playing as that class.
I don't know if anybody has considered this, but some abilities cost more than 1 level point.
And it's been confirmed that each level gives you ONE upgrade point, which you can use to buy ONE ability - EVERY ability will cost ONE point. But they may use more SUPPLY PIPS when activated.