So, we went from a cost of a bit over $3k/month for infrastructure, to almost $15k/month (would be more with AWS). Yes, you have to buy the servers, yourself at extra cost, but on Google most people run instances on Haswell/Skylake, which is >5 year old stuff, so a quick calculation for buying top of the line every 5 years (which for the first couple of years at least gives you faster hardware than on GCP) comes to about extra $2-3k/month. Also, we had 1 (very good) sysadmin and 1 other developer who assisted part-time sys-admining, to a cloud that has some extra bells and whistles, but requires 2 full-time sysadmins (we are temporarily left with 1 and he can't keep up). Part of the problem is that the whole architecture was very fine-tuned to run on our customized rack servers (it was doing happily for almost 15 years), so a lot of things did not translate that easily in the cloud. I guess if you have a small system, or designed from scratch for the cloud a single cloud platform person might be enough. Overall, there are some extra disadvantages beyond cost - e.g. Cloud SQL manages some things for you, but there is more lag compared to when our super fast DB server was on the same rack as the application servers, and other such little performance things that we could fine tune when we had control of the hardware.
