The big slow tanks problem is why WoT can't use the the bigger maps for the lower tiers but if it's solved then boom. The slower you are and the bigger the map. The more likely that the game will end with you still trying to reach the frontline.
There is a possible solution to the big slow tanks problem that has not been tried. These tanks were all meant to be mounted on tracks and taken long distances by rail. Some still have the rail bogie mounting points or Buffers and chain coupler on the model. https://en.wikipedia...d_chain_coupler
Speeds on ralis of 40 to 60 miles per hour for any of the the biggest slowest tanks were normal. Even the Maus was meant to go to the battle field on rail and then trundle a few miles to take out a bunker or turret. We need not depict a train engine just as we don't depict gun crew.
We have hard terrain and soft terrain but if railway tracks are made an additional terrain class then you could give the big slow tanks a big x2 or x3 bonus to speed on the tracks. Its not much help if you're crossing the tracks but great help if you keep your tog or Tortoise running along the track.
Add a few tracks to the bigger maps and have the slowest tanks zoom along the tracks passing the rest but THEY'RE ON RAILS! Everybody can guess where they would be.
A penalty for some other tanks on tracks would also be historically accurate. Some tanks could not safely drive over railway tracks without throwing a track.
At the lowest levels spotting distance will also matter. The last thing you want is a draw because the surviving tanks could not find each other. Changing the spotting distance with a map size bonus would fix that. Call it a weather effect if nessesary.