In regard to vehicles it's in my opinion more reasonable to divide between medium and heavy AFVs on basis of the compromise:
focus on (road) march mobility or focus on sturdiness in battle
The whole 8x8 medium AFV fashion was primarily about the race to Pristina, incited by Shinseki et al, secondarily about tight budgets in the many countries with smaller armies which wanted to modernize but lacked good AND affordable off-the shelf MBT and IFV choices and tertiarily about the widespread perception of tracked AFVs (especially MBTs) as Cold War dinosaurs.
It's so difficult to separate them nicely from light AFVs of the 10-15 ton range because the medium AFV (sans IFV) category is not founded on a consistent idea. It's a strange compromise. Wheeled APCs such as the Fuchs were nothing special during the Cold War, yet they were up-armoured, got better gun and lots of electronic whiz-bang and became the new hype.
To me there are three kinds of sensible army vehicles really small ones that are very agile and very easy to hide, very large trucks that allow for an unusually small vehicle count of formations and combat vehicles.
Combat vehicles (fully armoured, not just cab) again should be divided into a long-range wheeled category somewhat similar to French armoured recce, a medium tank (~40-45 tons, as the new Jap MBT) family for the greatest heat of battle and a carrier vehicle family supporting the latter (conceptually ~ stretched M113, SEP).
I can easily lay out better justifications for these categories than all the hype and buzzword rain about Strykers and other 8x8 MAFVs that I've seen published in 1999-2006 offered.
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On MechInf; the real difference is not about which ride they use, but about the combined arms setting they're expected to accomplish their mission (and what mission?).
Infantry fighting together with MBTs and indirect fire AFVs can and should be totally different from infantry that merely drives to a region of ops, dismounts and fights then without AFVs support.
The latter is not going to make very swift operational moves; a 150 km dash in one day through multiple defensive positions and surprised red columns is not to be expected. MBT cooperation infantry on the other hand is supposed to be rather reckless, to accomplish its offensive missions quickly and to provide security when the battlegroup is not on the move. It doesn't need much organic support weaponry such as Carl Gustaf or sniper rifles. In fact, an all-very light machinegun armament is a strangely interesting setup for them.
Any ride that can keep up with a mechanized battlegroup and not get shot to pieces too often by the encountered threats would be good enough, albeit not necessarily affordable.
Mechanised / armoured infantry that's not meant for quick offensive success with dismounted advance of less than 2 km is not going to have a consistent concept that meets operational needs.
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