It is entirely legitiomate to discuss the modlaities of a ballot, discuss how you define a valid ballot, discuss who is eligible to vote. All this I agree with and we definitely do not have the ideal system.

But that discussion should be independent of the outcome. Had the remain side won, would you still be holding this discussion and raising these points? If not, then its not really about the modality but about the result.

Between ballots there is a legitimate window to discuss and change the rules. Because then you can discuss in principle what democracy is, how you expect it to work and who you expect it to represent.

But trying to change the rules after the event is just being a bad loser.