I am basing the promise bottom-up, based on how many neurons are in the human brain, their connectedness and speed, and amount of computation those 3 pounds can be doing using the synaptic mechanisms we know about.
You are basing your skepticism top-down based on the results the science of artificial intelligence has shown to date.
It's a fair source of skepticism. There are 15,000+ species of just mammals, all of which have neural nets and exactly one of which have higher abstract reasoning communicated in a language with very strong innate grammatical rules - and that is humans.
However, we have 7 billion working specimens, a huge digital corpus of their cultural output, and their complete digitized source code which can be explored or modified biologically.
For me bottom-up wins. We can just try things until it works - which may be sudden/overnight.
At the moment I see a jet engine, feathers flying everywhere, and no flight. But looking at that jet engine, I just can't imagine it will take long.