Simply nerf allied TDs.
They over perform vs PzIV
They over perform vs T4 units
They over performed vs Tiger in team games and that lead to buffing to super heavies and creating the current mess.
I don't think that would actually fix the problem, though. Let's assume we nerfed allied 60-range TDs (M36/SU85/FF) by a decent amount:
1. The panther is still really expensive, and the added HP/Armor isn't really needed now. Instead, the STUG is now more viable, especially due to its higher DPS and range than the panther. Additionally, if you do save up the 490mp/180f (iirc), you might as well save the extra 190mp/50f and get a Tiger, as that's just a much stronger unit.
2. The brummbar is still going to impose a heavy micro-tax, and even then, it's only really good against blobbers. The P4 and Ostwind are simply better choices, since they're cheaper, arrive earlier, and don't require manually firing every shot. Also, axis doesn't need a "bunker buster", either.
3. The P.Werfer is still going to be situational. It's good against static infantry and support weapons, but because the rockets
always take a long time to hit, using it against moving infantry is tricky; you can't use it point-blank like a katyusha or caliope. This one also wouldn't change (at all) with a TD nerf.