Most formulas do take N in account.
If you are interested in comparing the distribution of treatments, it is often legitimate to use non-parametric procedures. But it is not in this case, as the random variables are discrete, although they may give reasonable approximations. As you seem to be interested in the mean, and not other aspects of the distribution, these do not work at all. Without SOME distribution assumptions, there are NO tests at all for equality of means. If the distributions are of different types for the two groups, major assumptions will have to be made.