Advantage of GCPRs over RTKs or other receptor protein kinases
I think GPCRs are evolutionary more older since tyrosine kinase signalling is relative recent evolved system. This could be one explanation for why their is more diversity in GPCRs

By the way GPCRs can actually signal g-protein independent, for example via B-arrestin. Also their are many types of g-proteins witch can all induce signaling via different signaling pathways. So GPCRS are actually quite versitile.

And then their is also a lot of crosstalk between GPCRs and RTKs