Or just build AT guns and arty to stop the Axis tanks, and rocket arty to wipe out the infantry (including motorized). Using cheaper, more basic units (those available earlier in the game) like AT guns gives you the option to research those units to higher levels, and upgrade them in the field, where they are needed. Just because you build an AT gun doesn't mean you have to use a level 1 unit all game long. When you bump that AT gun to level 3 and put it in a city, it can stop an Axis MT without the help of fancier, more expensive units like tank destroyers and attack bombers.
One of the biggest mistakes players make is to look at the research tree as a path to fancier units. Foot infantry leads to motorized infantry which leads to mechanized infantry. This leads to unfocused, ineffective research, always using level 1 units. But that's not how you win in this game. You win by making more effective use of manpower, which you can only do with higher level units, since manpower usage grows less sharply by research level compared to fighting strength.
One of the biggest mistakes players make is to look at the research tree as a path to fancier units. Foot infantry leads to motorized infantry which leads to mechanized infantry. This leads to unfocused, ineffective research, always using level 1 units. But that's not how you win in this game. You win by making more effective use of manpower, which you can only do with higher level units, since manpower usage grows less sharply by research level compared to fighting strength.