First of all, it was actually stated in the DBZ guide books that most lower-class Saiyans only had PLs in the 500–900 range. With the weakest of the low-class (including fodder civilians and child soldiers) likely past the 300~400 mark, therefore 500+ is a reasonable minimum for active fighters.

Plus, it's also heavily implied that plenty of low-level fighters were much weaker than Raditz or even a Saibaman (especially BoZ Goku), and they usually got sent to low-level planets as a result.

However, he's definitely far from the weakest warrior and is easily capable of conquering/destroying an entire planet by himself; which is still just above average and several times weaker than elites like Nappa and Vegeta.

So, I just wanted to correct you on a few misconceptions which you didn't actually try to debunk; I believe Raditz was most likely an upper low-class/mid-level Saiyan at best, and equal to a regular Frieza Force grunt.