You should explain more because the idea that the OKW AA HT is easier to replace than the USF AA HT is makes exactly zero sense.
How does vet 5 make up for the fuel shortage? Higher vet units don't give you more income. You have to pay for your medics and repair base. Resource conversion is stupid and does nothing but gimp you till late game, and the Schwer is AA aerial denial because it's OKW's most important tier building.
Allies are harder to play because you need better coordination, not because allied units magically do less dps or have worse armor.
And the most viable set up for 4's is 2 OKW and 2 Ostheer. Tigers are irrelevant in 4's against a good allies team, what you want from Ostheer is Elefants and indirect fire support.
In a 4's game, if both sides are making fuel caches, which by the way is harder for Axis due to Ostheer being MP starved, then the tanks will be hitting the field at the same proportional time intervals than they did before. The t34/76 will come in before the Panther like always.
You are forgetting how the map and space impacts the game. Allies for their early to mid and late game transition rely on map control early on and pressure. Both of these things are much easier to do when there is more space to work with. As you add players the maps only get so much bigger, and there are still only a finite number (usually not even that many) attack paths. For example on Kholudny there are many direcitons you can go for flanks and cut offs, but stack two players per side and now you are bound to run into enemy wherever you go in force. On a 4v4 map its even worse, while the map does get bigger the number of attack paths does not go up very much and so now players are forced into contact with each other. Less flanking routes and room to maneuver and exponentially expand means allies are forced into the grind of the defensive nature of axis.
In the most simple general case imagine there are 4 routes you can go around the map. in a 1v1 you can use 3 of the others to get around the 1 your opponent took. Now in a 4v4 each of those routes is filled with a player and you have to go through them. This means attacking heavily defended areas because each route has a concentrated force plugging the gap as opposed to in a 1v1 where there may be one or two units holding the flank.
The key concept here is that now Axis have a way of forcing allies into fighting on their terms at any point because everyone knows Axis has superior late game and the only way to stop that from happening is pressure and map control. Both of these have become vastly harder to get the upper hand on as you add players.
While it almost seems like this is a different issue, this is the same logic why instant pinning mgs were even more op in higher player count games. in a 1v1 you could run to another part of the map, but ina 4v4 you're stuck running into it no matter what direction you go.
There is absolutely no way of disputing this claim. The in order for allies to have better footing in the current game state, 4v4 maps would all have to look like a 1v1 on rezhev or Moscow