I think this is purely a statistics problem. Like all breakthroughs are actually _discoveries_ of things that already do exist or mechanisms that can be exploited somehow.
There is a huge amount of information flowing around us in realtime, and linking some thought/thing to something else, which then might have implications (subsequent discoveries) is statistics. We do have people with a better wetware so they have increased %chance do recognize something in front of them as well as linking it in a "novel way", but this is not really neccessary, it only increases %chances.
Even pretty radical things can be explained this exact way, up to having some sort of brain "damage" (or drugs like LSD) that changes mental pathways and have a %chance to be actually right and lead to discoveries, but also the %chance here is very low. (not every trip is a breakthrough in art/science, right?)... a bit like iE people that can smell sounds or link some natural phenomenon with an emotional situation between some people and write about it.
> peak human innovation
that might simply a nonsense question if you follow my previous argument. there simply is no real "innovation" - only "discoveries" of stuff. and we meatbags with very limitied/unreliable wetware at some point can't "progress" any more, but non-biologically flawed systems might overcome our limitations and do just that for us.
with our naked eyes, we cannot see things like infrared light, but it exists and some tools helped us to understand everything around it somewhat. now we're building more advanced tooling to get through the next plateaus - just like we have to build very sophisticated tooling to watch further into space or more closely into fractions of atoms, which in turn lead to more discoveries, and ultimately "innovation" we can feel in our lives.
the only thing I will 100% agree to is that a real AGI will be the _last_ discovery/innovation humanity will ever make - and that is a good thing - it means we finally overcome our biological limits somewhat.