BTW - this is why the jump from Prince to Monarch is the biggest difficulty jump in Civ 4: because, unless you are the Inca, the warrior rush does not work above Prince level.
Well, strange you said that, as although I never did warrior rushes, I also found the jump from Prince to Monarch the hardest one. AIs suddenly able to field massive armies, to keep up in tech if you have the same amount of land, which actually DECLARE WAR on you (That shocked me. I had never seen a SoD before.) and so on.
My first game on Monarch was as Sumeria - I char-rushed Spain, which was happily settling new cities and founding religions, not building any units
. Then I proceeded to Churchill, which was a lot harder - but elepults cleaned him up. With rougly 1.5 the amount of land of other AI's, I thought I was set for victory, but then Genghis comes in with his medieval SoD, reinforced by 2 units a turn on epic. I manage to beat him back, but then I notice 30 cavalrists and some other units on my border with Charlemagne, who declares war the next turn and takes a city.
Then I teched infantry and mauled those two jerks. Heh.
If I would have played on Prince, I would have just gone space or waited for tanks to clean up the map without any trouble.
Montezuma and the like also become more of a nuisance on Monarch. On Prince and lower he gets his SoD of jaguars ready by the time I have gunpowder - so he obviously doesn't attack me. On Monarch, however, he has the power to send a wave of chariots/jaguars towards you, which might lose you the game.
So I think you are right.