Just to be clear, everyone agrees on the advantages of QC and no one disputes that Google has built a quantum computer. Let me try to paraphrase the arguments.

1. QC needs qbits. 1 logical qbit needs many (tens to hundreds) of physical qbits.

2. We need Quantum Error Correction(QEC) to read cleanly from qbits. Current algorithms for QEC need about a 1000 logical qbits.

3. Current state of technology has only 50 - 200 qbits has very low signal to noise and the noise is inherent in the system (you cannot engineer it away)

4. The current systems, specifically Google’s, produce a sequence of numbers. It is possible to have a low complexity algorithm on classical computer which can produce similar sequences (i.e. pass the test for QC produced sequence)

4 is possible because reading from the qbits is noisy and such a noisy data can at best replicate a classical computer. So, the current state of the art, Noisy Intermediate State Quantum computers are not useful for any computation and we need to get to 1000+ qbits to achieve the supremacy. Of course, not everyone agrees that the noise cannot be engineered away or even if the noise is such a big deal.

If anyone is curious on how qubits actually work, I wrote an article explaining from a multiverse perspective: https://medium.com/@dangish/the-quantum-computer-explained-u...