>>43297671>>43297887>>43298078MKVI was to MKIV what MKIII was to MKII - never intended as a total replacement, just a specialized variant. While MKIII was MKII, with extra armor for boarding assaults, MKVI was MKIV but optimized for stealth. MKVI had with lower power requirements, easier field maintenance, smaller scanner signature, etc., but unlike the MKIII, due to the Heresy, all marks were in short supply, and MKIV in particular couldn't be made at all anymore. So loads more MKVI was made until MKVII was finalized.
MKVII is "better" than MKIV only from a logistics point-of-view; it can more easily be manufactured, more easily use replacement parts from previous marks, etc. but it would never have been rolled out in its current form if the technologically superior MKIV design was still viable.
Some of the features of the MKIV are of marginal importance; many details were developed in tandem with the Tactical Dreadnought project, but weren't really needed for Power armor, so they're not really missed.
Some other features are also less important due to the change in Space Marine role from mass battles to strike forces - such as MKIV's far superior power efficiency and cooling, allowing it to be used to its full capability for far longer (weeks rather than hours) without having to power down or becoming too uncomfortable for even a space marine to wear.
