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Correct, but the increased attack stat on the guard unit isn't going to make a ton of difference, which is probably why the answer to this question wasn't already obviously apparent. You're talking about ~18 for guard vs ~15 for infantry as your modified attack value in the early game. Then you have to consider all the other factors like leader attack/defense, terrain, die roll, etc. which further dilute that gap.
It's not even that big. By the time you have all of your 1850 inventions, it's only 19/16 versus 17/18. Guards benefit from their extra maneuver, not from their tiny amount of extra attack value. Even then, I hesitate to call them "worth it". They're still tougher than anything else you could put on your flank if you outnumber the enemy though.