You are forgetting superior infantry with higher model counts that fight alongside this armada. Then we have the indirect fire that is always around, which is more effective against ost lower squad sizes. If you get 2 panthers, you have no room or resources left for AI vehicles, which you desperately need to fight the higher model and more effective infantry of the allied opponents. If you get AI vehicles, you have no room or resources for 2 panthers and your AI vehicle gets bullied by TDs and you still can't fight the infantry hordes.
the panzerwerfer is great for fighting vehicle and artillery spam... plus the only real arty that poses a threat to grens are either rocket arty... tanks scotts... or pack howis...
rocket arty can be suicided at by panzers along with scotts...tanks can be pushed back by AT guns... and the pack howi can be counterbatteried by the panzerwerfer...
the best strat to do when the enemy builds 2 SU/jacksons is to either
1. get MG-42s and creep em forward with panzerwerfers to kill enemy arty
2. creep grens forward but keep them separate to cap territory...
3. move the AT gun forward to dissuade tanks from killing ur stuff
4. laugh how at least 30% of their popcap is consumed by AT... while you counter em with basic infantry and artillery