I don't really see the heavy classes being that powerful.
Just testing them on myself in the tutorial thing, the light spinfuser does 550. The spinfuser the soldier has does 650. The heavy spinfuser one of the heavy unlockables gets did 700. It's possible the heavy armor blocks more, but I've yet to be one shot by anything. Takes several shots.
Now the fusion mortar thing does 1200, but it isn't easy to hit with that due to the delayed fuse.
Seems to me the starting classes are actually the best. They get energy packs letting them have more energy for flying, and their guns do pretty good damage.
I unlocked the pathfinder, but didn't find it that fun. Having health reduced to a mere 800 made me much more squishy, and the speed increase wasn't all that noticeable. I was regularly getting 150 on the medium, and about the same effort was giving me around 180. The little extra speed might help with grabbing a flag and trying to get away, but most games both flags are constantly taken and it's rarely possible to do a speed capture due to your flag not being there.
What I did notice is the drop in energy switching away from a class with an energy pack, the lower energy kinda sucks. Since everyone is using explosive guns you're better off having a little bit of extra flight time, because the first person to stay on the ground is gonna go boom.
Some of the classes just don't seem appropriate for the fast, fly-around skiing environment. Like one class gets a shield that uses energy to block hits, but I've yet to see a case where I'd want to turn a shield on instead of use my jetpack. I guess for attacking those turrets it might be handy.