"Well optimized MySQL" sounds a bit like having a really attractive liver cancer. Cloud services expand your options and it's worth pondering them. Don't ask what is the best MySQL, ask for a given amount of items I need to store and recall what is the best server OR SERVICE that could do it? MySQL on bare metal? On virtual machines? RDS? Cloud Spanner?

Do cloud providers increase your ability to choose scale-up instead of scale-out? Instead of your sharded and replicated MySQL that is almost inoperable and never seems to maintain consistency, would you be better served with one gigantic database? Sure it costs $13k/month to rent one from Google but it costs a quarter million to buy one from Dell. These are all aspects of the decision-making process.

MySQL-RDS is the AWS service which I felt gave me the least value for the dollar. (Except for the OpenVPN server which went nuts and did an obscene number of I/Os against EBS which ran up my bill)