> My intuition is the latter- it would be a surprising coincidence if some complicated electro-chemical reaction behavior provided an essential building block for human intelligence that would otherwise be impossible.

Well, I wouldn't say impossible: just that BMI's are probably first. Then probably wetware/bio-hardware sentience, before silicon sentience happens.

My point is the mechanisms for sentience/consciousness/experience are not well understood. I would suspect the electro-chemical reactions inside every cell to be critical to replicating those cells functions.

You would never try to replicate a car never looking under the hood! You might make something that looks like a car, seems to act like a car, but has a drastically simpler engine (hamsters on wheels), and have designs that support that bad architecture (like making the car lighter) with unforeseen consequences (the car flips in a light breeze). The metaphor transfers nicely to machine intelligence: I think.