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What are you so afraid of mages on the second week for? You shouldn't just sit around and do nothing.
But seriously, a mage on day 121 is practically an overpowered force, BUT – it's a gamble, and both sides risk something, because a mage on day 3 will defeat a warrior in 90% of cases, as he will be firing 5+ angels for 4-5 rounds, while he will be taken down to zero in 2 rounds.
This is a similar gamble to Kir' vs. Shakti: either the supreme one will kill him, or he will have trouble catching the runner later; or castle vs. swamp: if you don't kill Tazara with a small unit, you will break all the spears on his armor later.
It all depends on whether there will be a quick advance on day 2 – and this already depends on how the generator distributes things, and it is not always fast, especially if the roads are slow.
So, you can add some randomness and intrigue – I don't think mages will become more cheesy than Shakti. After a couple of cons, he will be ready to face anyone on day 121.