I would say, "YES". I does matter from both a lethality and survivability viewpoint - I'm talking air-to-air here as that will be a very important role for this platform.
The ability to get to high altitude and high speed has a massive effect on energy at launch for, say, AMRAAM. That should be ONE of the big advantages of F35B over the old Harrier/SHAR. Any reduction in that will adversely affect lethality and "first kill".
Sustained g affects the aircraft's ability to evade/defeat incoming air-to-air missiles and SAMs. I'm not talking about close-range stuff here (although that is obviously an issue too, should you choose to go in close and "mix it"), I'm talking about long range f-pol and a-pol manoeuvre, designed to deny or defeat the enemy's firing solution or to defeat the missile at range, soon after launch, kinematically. Unless you really believe that stealth will truly keep you 100% safe.