Honestly, that's how I do things, up to lvl 22, when I turn it off and clear it and the next to manually.
Still didn't manage to beat L28, and with how expensive those missions are, I see no point in trying to retry it over an over and over again hoping for good enemy RnG when it comes to tanks they pop out.
Maybe after I get my tanks to L28-30 the map will be more feasible but at this point I am happy enough that I can relatively reliably take on L26 which still is not auto win since if you get a bad spawn you get troll face steam rolled over regardless.