Plus, it is convenient to sync photos directly from mobile to the cloud without the need to set up syncing software or do periodic transfer/backup from mobile to PC.

…that wasn’t the point? Keeping possessions safe is the responsibility of the possessor. If you keep them all in one place with no backups, you can lose them more easily.

And by the way, you don’t actually know the probability of a random person losing access to a Google account vs losing physical mediums, let alone how many of those cases were cases where their only photos were stored there. It’s obviously different from person to person, and maybe you can estimate that one is safer than the other in individual cases, but you can’t extrapolate that and say it applies in every person’s case. But the GP was referring to cases where it was implied the only copy was stored on the cloud.