I see arguments like this as a form of the naturalist fallacy. Not every aspect of the original TCP/IP design is worth preserving and exploiting. We don't need an URG pointer. We don't need IP source routing (really, we don't need the IP options we have now). We don't need a "length" field in UDP. &c.

TCP should have been built on top of UDP, as should ICMP. The IP "protocol" field doesn't do us much good. I don't think we should fret too much about not exploiting it.