birds fly after millions of years we have rocket ships and supersonic planes after decades. horses run at tens of mph we have wheeled vehicles doing hundreds of mph after decades.
Absolutely not an existence proof, but evolution appears to have concentrated on gooey carbon and left multi order of magnitude performance gaps in technologies involving other materials in all sorts of areas. The expectation would be that there is nothing magical about either goo or the limits evolution has so far found when considering intelligence.
Indeed, silicon computers are WAY better than human brains as adding machines, doing megaflops and kiloflops with great accuracy from a very early development point, where humans could do only much slower computation. Analagous to what we have done with high speed in ground and flight i would say.
Comparing megaflops performed by the silicon hardware with symbolic operation by the human brain is comparing apples and oranges. If you measure the number of additions and multiplications performed by the neurons (yes, less precise but more fault tolerant) you will arrive at a much higher number of flops. Think about mental addition more like editing a spreadsheet cell. That includes lots of operation related to updating, display, IO, ... and the addition itself is an insignicant part of it. Same if you juggle number which actually represent anything in y...
If Strong AI turns out to not be possible, what are our best expectations today as to why?
I'm thinking of trying myself at writing a sci-fi story, do you think exploring this idea has positive utility? I'm not sure myself: it looks like the idea that intelligence explosion is a possibility could use more public exposure, as it is.
I wanted to include a popular meme image macro here, but decided against it. I can't help it: every time I think "what if", I think of this guy.