It would help if the nature of battlefields at different TLs were outlined, discussed, and then doctrine necessity explained.
My personal headcanon for a TL15 Imperial Army soldier:
battledress constructed at TL15 - cheaper than TL14
FGMP-14 constructed at TL15 - cheaper than TL14
the battledress has an AI battlefield computer, map box, radio, radar, ladar, radio jammer, EW suite, point defence interceptors, a dedicated robot/drone network, a rapid pulse laser point defence system, smoke/chaff dispensers, decoys, anti-laser cans, chill cans, stealth, active camouflage, anti-personnel laser
this is necessitated by the nature of the battlefield - the soldier has to be as self sufficient as possible because meson artillery, hunter robot/drones and the like make concentrations of troops easy targets. Each soldier carries an electronics array compliment that makes the electronics carried by something like an F-35 look like a valve radio...
the armour is as mobile as possible because movement is crucial to survival
the countermeasures and defences are proof against most robot/drone/remote munitions provided they do not attack in numbers that can overwhelm the defences
the "cloud" of robot/drone wingmen provide greater battlespace volume coverage, more lethal weapon options than can be carried by the suit alone