I agree with 99% of what you’re saying…but Echidnas have bigger prefrontal cortices than we have. More to the point, you’re sounding a little teleological when you ask “What makes homo sapiens the culmination of the process of evolution?”

I don’t necessarily think any living thing is more evolved than anything else on Earth. While we were busy learning to dance and make bladed weapons to fit our shiny new niche, sharks and ginkgo trees were keeping to niches they had been in for quite some time. The changes a stable old niche tends to foster are a lot less flashy, so I presume their evolutionary paths focused on practical but painstaking items that a species only gets around to by avoiding the distraction of newfangled fads like bones and flowers and such. My guess is that they were both incrementally improving on their exquisitely flexible, powerful, and fine-tuned immune systems.