Most, if not every other competition in the world, have set rules, that EVERYONE abides with.
Why is the FA Cup different? Why do we have VAR in some games, when the majority do not have it?
The competition should be played on a level playing field.
Some teams were eliminated because they didn't have VAR and some were eliminated because there was VAR.
IMHO if one game is unable to use VAR then NONE of the games should use it.