Maxims are at their annoying best when spammed and when used in opening build orders. Being in the same structure as at guns also exacerbates the problem.
Don't get to fancy with the solutions.
Delay their arrival, adjust reiforce cost, increase pop cap and much of the problem is solved.
If you want to be bold remove a-move from all team weapons thus increasing skill cap.
Personally i see maxims as a damage multiplier not a suppression platform. Maxims should be used in conjuction with other unit to make up for the lack of damage from cons etc.
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They are already weakest for the cost.
Doubling how long it takes to make them, doubling their cost, and doubling their popcap will
only bring about one thing : That they stop being used entirely.
The problem is that they are so weak that they only work when spammed.
Also consider that when you have Maxims, you don't have Penals.
Germans also dislike Penals.
Wouldn't it be sweet if Soviets could only spam Conscripts?
Please note conscripts don't scale well at all, and that their molotov got nerfed into ground
already (OMG that windup time).
(Would it kill germans if that ridiculous windup time was fixed) ... Actually it would, but...