Of the last 5 years we have been in the Championship for 2 of them and Brighton have been in the PL for 5 of them. Not exactly comparing like with like. Also, you have now added the 'net spend' caveat' to your assertion as opposed to just spending shitloads. It is kind of convenient for your argument that we have just sold a player for a record transfer fee to an English club of 100m. The actual numbers as per transfermarkt are below. If you don't think we are massively outspending Brighton you have your head in the sand. Look at our spend on players since we got promoted.
EDIT: That doesn't include significant loan fees for Tammy, Bolasie, Tuanzebe (twice), Mings, Barkley, Drinkwater, Onomah, Johnstone, Snodgrass, Carroll and Reina.