The whole point of that part was to show that it's really alot more up to mapper itself how to 'balance' things in the face of realism as much as it goes against itself aswell.
Yes. But unfortunately level designs are often tampered with by those with little understanding of what TO&E means or what an OoB might be or what it means to research an actual battle and subsequently develop a scenario for the battle. The numerous half-assed clones of Orel and Debrecen being great examples of the worst sort of level tampering. I personally would like to see password protection of *.rom files to keep potential meddling to a minimum and to greatly reduce the numbers of half-baked clones we are subjected to when playing this game.
Unless we're talking some specific odd situation and let's say a company of tanks vs another company of tanks it would be single model of tanks only. In terms of TOE and OOB that's quite realistic, and hence we run into the realism relative to what issue.
In general yes. Certainly the trend in RO\MN\DH tank level design leans toward the exceptional OoB rather than the typical in this regard. by that I mean we tend to see what would be considered rather rare historical OoBs as the norm in RO game levels -- particularly on tank maps. Which is extremely humerous considering how nit-picky tank gamers are about wanting their game to be "realistic".
But of course there are numerous historical examples of hetrogeneous vehicle mixes for particular battles -- and I mean this in terms of tactical level rather than operational level force mix. This is particularly true when looking at cobbled together German Kampfgruppe. A good example might be Kampfgruppe B