I'm not expert enough to chime in but the people that I respect on this subject agree with you. I would also be surprised if GPT-5 was miles ahead of 4. The airplane of today is extraordinarily similar to one from 50 years ago.
I think the biggest improvement we'll see in LLMs is (we normal people) finally getting access to what exists but which we currently don't have access to, and the slow leak of these technologies into our day-to-day.