Definitely relative - the idea I'm trying to promote here is that with the right balance, you could have the fps players as infantry preying on the noob mech pilots, while the MechWarrior gods would be able to bring the balance closer to the infanrty-frying, tank stomping action we all know is the natural order, at the cost of some concentration and situational awareness.
The idea is that the infantry & vehicle players can concentrate on the whole scene, while the mech pilots are more likely to have battlefield tunnel vision due to all the blinkin' lights, and have enough attention left over to concentrate on maybe two enemy mechs... this then gives infantry etc. a chance to sneak up and leg 'em or swarm them while they aren't looking.
With the simplicity of controls in, say, MW4, the gameplay balance is tilted overwhelmingly towards the mechs, as the mech piloting takes very little concentration. Trying to redress the balance by making mechs less powerful or easier to kill would ruin the premise, IMHO. Making mech piloting a challenge, on the other hand, fits perfectly with the game universe. Perhaps not by overwhelming the player with controls, maybe some trickiness with the movement dynamics would do the trick - taking damage when running into buildings at 100kph, for example, or tripping on vehicles.
I'm not advocating a system which would make the 'good players' practically invulnerable... thats what being in a 'Mech is about, after all. The idea is to make anything less than an uber-expert Mech pilot slightly less invulnerable, so that the infantry and vehicles have more chance than the average greasy smear on the pavement.
What I'd be expecting, on a scale of 0-10 for invulnerability, maybe expert in a mech=9, average player in a mech=8, noob in a mech=6, vehicle=4, Battle Armour Infantry=3, unarmoured guy=0 or something like that, as a rough guide (not accounting for weight classes

). If a mech warrior fanatic in a medium mech gets taken out by a set of 4 demolishers acting alone, I'd be rather skeptical, but if piloted by a medicre player who gets in too close, has to stop to avoid a building, and gets plastered by half a dozen UAC/20 shots - that I could see.