In an ideal world there would be massive testing for all new gear: a "consumer reports" approach. No advertising in the magazine.
Magazines who produce board test for their readers, I suspect, want to be fair but must consider trashing their advertisers product may mean alienating an income stream. On the other hand what are the alternatives for advertising without magazines?
The fin issue for board performance is huge. Used to be fins were afterthoughts for board producers: give them something but we know most will buy an after market fin anyway. Today the fins you get with a new board usually are very good. Big improvement to board packages of yesteryear.
So a board review in any magazine gives you an opinion about performance right out of the box. Doing more testing to find the right fin to make a board perform better upwind would overwhelm a magazine test. Hell, isn't this what racers do? Spend a zillion dollars on fin quivers to gain a performance edge on the race course.
The fin is so important to a board's performance upwind and for early planing that comparing 2 boards with different fin lengths of more than 4 cms. seems unfair. But the insight from the first post is what is needed to read between the lines and get the most out any review you read in any magazine. Testing budgets for magazines will only take you so far...