Question about watt per sf

Not sure if this is the right section but it seems like noob question

Ive read 50w per sf is optimal so my question is why are led lights in the 400-600w range marketed towards a 4x4 or even 5x5 space?
Example spiderfarmer 4000 and marshydro FC 4800 are for a 4x4 space. Both of these lights are around 475watts that would put me at 30w per sf and that is waay under the 50. So does this rule not apply to leds?

Better to look at par maps for any particular light you are interested, then search the forums and look for people who use that light for the same footprint that you want to see how they perform. Those old watts/sq foot rules never really worked well.

700-900 ppfd.

From what I've read it has to also do with the quality of the LEDs.
30W/ft2 for high quality like 301B/H.
Up to 50W/ft2 for lower quality LEDs.

The wattage per sq ft was pretty useful a many years ago when I used hps and floros. I still use floros in early stages lol. However that was when you had this hood that had to reflect light for coverage and cool itself because it was pretty hot. Phones didnt have nice sensors and extra gear cost more like par readers. Now you have lights that are flat and more efficient. It's much easier to use lux and footcandles now