I think its a lot to do with actually watching Brighton play. They play like a top 6 side already.
I do understand your point, its a lot like watching Swansea or Bournemouth in the past - pretty football but also pretty ineffective when really put to the test. Similarly, how many (in general, press etc) were crowing about Chris Wilder last year after how he had Sheffield Utd playing?
However, watching Brighton there is something different, IMO.
Firstly, their defence/defending is VERY good. And this is the first failing of the 'pretty' teams above. Brighton build from a properly solid base.
Secondly, they average (last I saw) over 50% possession over the season. Which means one of two things to me - either teams are sitting back more against them (and yet they still famously create a lot of chances), or they arent sitting back so much which says Brighton are playing through their press well.
Thirdly, the chances. Im no great lover of xG, but it is shocking just how many high quality chances Brighton create and fail to take. Again, watching the game it is very apparent this is not a statistical funny - where its technically high quality chances per xG but in reality its nothing of the sort - it is genuine high quality chances, and lots of them. I watched the Leeds game at the weekend, Brighton with a half decent striker would have won 4-0 comfortably.
As it is, they won 2-0 comfortably. Biesla gets hyped so much, and yet Potters Brighton comprehensively outplayed his Leeds on the day (twice this season I believe). Sacrificed some possession, but left Leeds without a sniff all game, dictated where the game was played, and created enough chances to have absolutely spanked them.
Its not plucky underdog stuff, IMHO, its the exact sort of stuff that top teams do to succeed - yet with players not near the quality of squads like ours.
There is a great cohesion to the side, achieved rather quickly upon arrival - and in stark contrast to Hughtons style - suggesting excellent training methods. This team moves as one, and has that Man Cityesque ability to move in a way that all the passes look easy and obvious, but are somehow so difficult to play against. Also that City like off the ball forward running (something we have been criminally poor at for years).
I do understand where you are coming from, I just dont think you point stands in this situation. There is just too much quality about how Brighton play to ignore what Potter could do with a club like ours. If he simply implemented his style here, I think we would be something really special - not falling into that "wont work if teams sit back" trap, and thats before seeing what he might develop with the added quality we have.