>emergent >sufficiently complex
These can be problem words, the same way that "quantum" and "energy" can be problem words, because they get used in a way that's like magic words that don't articulate any mechanisms. Lots of complex things aren't sentient (e.g. our immune system, the internet), and "emergent" things still demand meaningful explanations of their mechanisms, and what those mechanisms are equivalent to at different levels (superconductivity).
Whether or not AI's being networked together achieves sentience is going to hinge on all kinds of specific functional details that are being entirely skipped over. That's not a generalized rejection of a notion of sentience but of this particular characterization as being undercooked.
You are really underestimating the complexity of the human brain. It is vastly more complex than the human immune system and the internet. 1 cubic millimeter was recently completely mapped and contains 57,000 cells and 150 million synapses. That is about 1 millionth of the total volume of the brain.
The immune system has 1.8 trillion cells which puts it between total brain cells (57 billion) and total synapses (150 trillion); and contains its own complex processes and interactions.
I’m not immediately convinced the brain is more complicated, based on raw numbers.
I don't believe anything in my statement amounted to a denial of the stuff you mentioned in your comment.