I've seen Soviet players steal USF tanks, people tank-trapping off their ally, indiscriminate artillery fire hitting friend and foe, and even an OKW player blowing up another player's medic truck because the truck's owner lost a KT. I've even seen an incendiary strike on an Ostwind that was drove right next to a USF Major, the US player killed the Ostwind but lost most of his forces to his teammate's indiscriminate firebombing. If you think 4v4 players won't destroy another person's cache in order to make one that actually benefits them, I think you're giving them too much credit.
Half of what you're describing is teammates trolling each other and the other half was bad coordination or accidental friendly fire. Neither of which is a reasonable objection to the possibility I outlined. You're making out like it's going to be some kind of common place thing that will significantly impact team games. That it won't work because killing each other's caches will be "part of the meta" rather than one or two dick players who are fucking with their teammates (and yeah I've seen someone drop an arty strike deliberately on someone else when we started losing once so I'm aware it can conceptually happen).
I'm not suggesting caches don't benefit teammates, but that they benefit teammates less than they benefit themselves. If this suddenly turns into a meta where significant numbers of people are killing each other's 200mp investments (that's almost the price of a squad) over something so short sighted, I will eat one of my 8gb ram sticks.
The reason OKW is so beastly in team games is because of two factors, the first being that it's significantly more difficult to outclass the whole enemy team than it is to outclass one player - weaknesses in build orders become drowned out by the number of players, single mistake from one player get compensated for by his teammates. Thus the idea of the Allies leveraging their (mainly USF based) early advantage becomes more difficult - the majority of games go to late game. The second is the proliferation of resources that OKW was never really balanced to be able to receive. I mean, you could just make it so caches don't contribute anything to OKW in general, but I'm sure the community would whine even harder about that.