Try taking a stingray to a band jam session and see how it sits in the mix. It is very different than by itself. I never noticed the issue until I took mine to practice for the first time.
I've recorded with them tons (stingrays I mean), as have many much more important bassists than myself ;-)
no issues there that I can see which would apply to all stingrays.
It IS quite possible that the G doesn't cut as much due to mid scooping the controls (which I believe some stingray players do, specially so on 2 band models by turning everything up too far). And compared to a fender precision which is mid-forward imho in a strong way, the stingray will definitely not cut through in a band setting as well, but then it sounds completely different too overall.
Edit: Stingrays have a smiley-face curve which naturally reduces output of fundamentals and first harmonics on the G string. it's part of their tone. eq is a simple thing - it can't only affect some strings unless of course you have separate pickups for each string.
I believe the mid cut introduced by turning up the bass and treble controls does coincide with the root frequencies of the G string (with a large margin above and below), which is why slapping is so fun on these things.
Try turning the tone controls all the way down and see how it sounds. or, at most put each on about 15% to 20% of the way, so almost off. Not saying to play that way all the time, but to experiment and start with fresh ears like that to see if the same problem exists.
It certainly doesn't with mine - I've checked after reading all this stuff in other threads on TB LoL