The main consideration when comparing weapons, armour and the like.
If you are running around on foot the biggest weapon you can lug is likely to make a real mess of someone else running around on foot. Caveat: basic powered armour allows you to overcome the limitations (speed and dexterity mostly) of the heaviest un-powered armour. The heaviest powered suit (tactical dreadnought armour) moves past that point, but it is of higher tech level, is ponderous- probably worse than medieval plate, requires extensive backup, power and technical support and is too heavy to be used where a normal person could walk. (no ladders, swamps or light transports)
A weapon you can quick draw and dual wield should not be easily capable of taking out a vehicle. I’m not buying the inferno pistol having the same anti-armour capability as the multi-melta.
Armour that is so heavy it requires tracks (if that is your intention) should not be susceptible to weapons that are portable by normal un-powered troops, unless you get lucky. At very least they should be more like man-portable artillery. Effectively immobile, not just move or fire.
I suppose the counter argument is that in weapon-armour evolution it is possible that one side renders the other irrelevant. Why would you not just equip everyone with melta-guns, if they function in the way represented on the current 40k table-top?