Actually the way my heavy tanks work is I deploy them first and then depending on map and enemy spawn (especially in PoC). What usually happens is my mediums have much more range so they actually stop to shoot further back then my heavy tank so the aggro gets put onto my heavy and even if it doesn't any additional enemy reinforcements will tag the heavy instead of medium. In this way some damage gets rotated or if i deployed TD after Heavy, things die fast but thats cause im using fv4005 stage 2 which has fast charge rate of skill which is 80% dmg increase and 100% pen.
Regarding my emblems I have mostly 3* couple 4* and some 2* which i deem not worth to replace without a 3* equivalent either due to damage or stat stacks. I have all emblems at +10 except 2* ones