Yeah, last time I was there, that was a Friday afternoon, so basically the height of peak time as far as fare evasion is concerned for them. To be fair though, that is a useful tip, and if I am taking a journey which officially requires a change at Brighton, I will probably go at Weekend if possible. I am not a fan of going through queues, particularly queues created for needless reasons mentioned directly below in this same comment. Fortunately, I have often been able to avoid Brighton, and on a recent trip from Bognor to Maidstone, I avoided Brighton by going via Redhill and into Maidstone West, when the alternative would have been to go via Brighton into Maidstone East.
That would work just fine to be honest, but the problem there unfortunately is that for GTR, that would cost money, and I suppose for them its cheaper to get in cheap, (possibly) agency staff who aren't trained to check tickets, and just are told to turn people away. If they were there for reasons such as security, say if there had just been a series of fights at Brighton station, then that is money well spent. However, when I was there, the only thing the chap was doing was turning people away from platforms 3-8 (I arrived from P2), including an old fellow with a suitcase, probably heading to Gatwick Airport, and forcing him to queue for one of ~6 exit barriers, which won't be enough at the height of peak time considering how crowded trains are in the final leg of a journey into Brighton, particularly from the Coastway lines.
They didn't seem to be checking tickets at all, just sending people to a ticket barrier where someone intending to dodge as much of a fare as possible will just resort to buying a ticket through Brighton between any 2 of the 3 lines, and dodge the rest of their fare. Bringing those staff into Brighton where there are already ticket barriers where with already significant staff presence is just a waste of money, and it won't stop people from squeezing through a barrier, or over or under given that they are not that hard to get through, given that there is already a reasonable chance you would get caught red handed anyway.
A better use of those staff would probably just be to send them to quiet stations where people can easily get onto a train without a barrier, like the current unstaffed stations, and that may put of some of the fare evaders. In places like Aldrington, if they see someone walk onto the platform without using the ticket machine, they can demand to see a ticket, and otherwise order them to buy a ticket or threaten them with a penalty fare otherwise. That could help to prevent some people dodging fares from boarding those trains into Brighton in the first place, and that would partially solve the problem of mass fare evasion. Of course though you cannot ever check everyone, which is why the solution isn't perfect.
In general however, there is no easy fix, because solutions like barriers at every station or staff at every station won't work, and no matter what train companies do, people will always find creative new ways to dodge as much of their fare as possible, no matter how many resources are thrown at trying to deal with the issue.