Hammer is supposed to be about taking the fight to the enemy. Hulling down to increase output is very much the opposite of that. Good idea but not thematic. It needs to be able to make use of mobility to contrast the Churchill.
Exactly, the point is to give it a twist instead of just making comets "premium cromwells". If comets mobility gets slightly buffed and this new stationary combat is enable, swapping with relatively low cooldowns, you achieve great firepower trading the most notable aspect of hammer tactics (mobility and punching hard) and when you are done get comet mobile back again and smash that rush mode it has to put it safe.
Its a harder, micro demanding way to get comets outperform but this way you ahieve two distinct things. First comet spam is harder (hey they get massed in teamgames) and also comets get a very dynamic profile, paired with all the abilities it already has (smokes, grenades, rush). It becomes a premium versatile tank. Stats can be tweaked up/down to make it perform well
Comets get risky and high versatile tactics and anvil gets slower but more reliable ones