this isnt a mechanic exclusive to relic. warcraft 3 had increasing upkeep based on army size as well. the intention is make it harder to reach pop cap. having a constant (or near constant) income despite your army size would result in armies growing at a linear rate. just look how fast armies grow at the beginning of the game. it would do that for the entire course of the game.
the current system slows down the growth rate as armies grow. i wouldnt consider this a penalty. do you see any high level players sitting in the base with no units just so they can keep their mp income up? no, because its not an advantage.
just watch lenny's stream sometime. he frequently spams cons. he takes huge numbers of losses, but it doesnt matter because reinforce costs are so low. now imagine having little to no upkeep. it would only promote more spamming and blobbing.
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Relic Entertainment
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