I think two things are at play here. First, it is reasonable to demand that manufacturers supply a good fin that suit the board, ie is a good all round fin for the board both in terms of sail sizes and in terms of type of sailing. It is also reasonable that magazines first and foremost test the boards with that fin. The only alternative to that would be if boards were not delivered with fins anymore. Since OEM fins nowadays are very good and the price the end customer pays for having them delivered with the board is MUCH lower than the price of a comparable aftermarket fin, I think this option would be stupid.
The other thing at play is that to "fully" characterize a board, one need to test how it responds to different fins. It's just as important as testing with different sails and in different conditions.
But I think standardizing size/area is going to far. Even within rather narrow groups of boards and with a given sail and rider, two different board designs can work their best with different fins. I think it is reasonable to let the manufacturer chose the "main fin". Then testers need to get more open about the fin choice and how that might reflect the performance and preferably also do at least some testing with different fins. That would be reasonable even within the limited time available.