Well in a completely combat oriented playthrough you won't really need all the stealth, hacking and what-not upgrades. Just strength, recoil, typhoon, dermal armour and perhaps some energy upgrades.. I think you'd get more than enough xp for that?
Stealth requires much more to be unlocked and it's probably why they went this route.
I agree, In the last mission I spent a lot of time sitting somewhere out of reach and recharging.