Arsenal will probably actually have the minimum number of 13 players, but they san say that the likes of Saka, Martinelli, Tavares, Nketiah and Smith-Rowe don't count as they almost certainly aren't named players in the squad of 25, simply because they don't need to be as they were 21 or under at the start of the season. If you don't count those players then they probably do have less than 13 available, but that is a nonsense.
Suporters now lose out on travel cost, hotel cost, etc, local pubs and cafes lose out on revenue, having probably got extra supplies in for a massive local derby, and it really just isn't right.
That is a loophole that needs to be closed then, it's just plain wrong.
As to the detrimental effect it has on supporters and local trade - completely agree with you.