You can usually get 2 shermans by 7 CPs, so you should be able to completely crush his volks blob with them. If you can kill the flak HQ after he retreats, its usually GG, and mech arty really helps with that.
I try to spend the least resources possible on jacksons. If you kill the enemy armor, it becomes a upkeep sink and a fuel sink of 125 fu. I prefer to have 2 shermans before I invest in a jackson, especially since 2 shermans can finish an engine damaged panther easily.
Jackson can always be used against trucks and a rule I go by is always assume OKW has a panther coming, and with 2 Sherman's your day can be ruined pretty quick if the guy gets some lucky bounces or misses.
no ones stopping you from going 2 Sherman 1 sherman 3 jacksons whatever to priest. It really depends on who you're playing or how you like to play. Just make sure you have 2-3 T4 tanks before calling the priest so it's protected well
Edit can you post a replay of you using Mech in 1v1?Not just against this pak strat. I'm interested in how you find truck setting up etc. I don't wanna risk ruining my win ratio even more than it is by trying it out myself lel