The strongest evidence that H&C is not Quirrell seems to me to be how much more amateurish he is at manipulating people than Quirrell is. I don’t believe it would have taken Quirrell dozens of iterations to realize he ought to change his appearance. It probably wouldn’t have taken him one.
I have no strong opinion on whether H&C = Quirrell, but Harry has already remarked on Quirrell’s facility at playing different roles.
The strongest evidence that H&C is not Quirrell seems to me to be how much more amateurish he is at manipulating people than Quirrell is. I don’t believe it would have taken Quirrell dozens of iterations to realize he ought to change his appearance. It probably wouldn’t have taken him one.