Fair enough, but none of the following was true until recently:

The production proof-of-stake network has been running in parallel for a year and a half, with 10% of all ETH locked up in it.

What's left is the merge with the rest of the network. They've tested the merge on every combination of five execution clients and five staking clients.

They've done about a dozen large test merges on copies of the live network.

They've done the merge on a large long-running testnet used by applications, block explorers, exchanges, etc. Essentially it was a practice run by the whole ecosystem. There were a few minor glitches but it worked well enough to be a success if it'd been the live network.

There are two major testnets left, and if those merge successfully then the next step is production.