I somewhat agree… !
One reason to not pick the mainnet block at the same time as testnets is to not set expectations in the community too early. IMO what we did for London, to wait and make sure the testnet deployment went smoothly, was the right approach.
The reason for this is that the things which have the highest likelihood of breaking are the “large initiatives”, and they are also the ones we would be most likely to delay the fork for. For example, if we had found an issue with EIP-1559 on the testnets, it probably would have been worth delaying London by 1 month to fix it.
OTOH, if we find an issue in a “small EIP”, then maybe it’s not worth delaying the fork. It’s also worth pointing out that in some cases, removing an EIP can be more work than fixing a bug, because we need to test for non-inclusion, to not end up with consensus issues like we saw on OE in Berlin.