Maybe you should skip bashing modern devs and people who learnt from online courses when the parent poster is the one in the wrong. Unless InnoDB has a particularly bad implementation of disk backed temporary tables almodt all disk IO should be done in the background so the latency cost should be small. I recommend benchmarking on you particular workload of you really want to know hur big it is.
I am an old-school developer with a computer engineering degree but many of the old famous devs were self taught. Yes, if you learn how to code through online courses you will miss some important fundamentals but those are possible to learn later and I know several people who have.
We have excellent metrics between PMM and AWS Perf. Insights / Enhanced Monitoring. I assure you, on-disk temp tables were to blame. To your point, though, MySQL 5.7 does have a sub-optimal implementation in that it kicks a lot of queries out to disk from memory because of the existence of a TEXT column, which internally treated as a BLOB. Schema design is also partially to blame, since most of the tables were unnecessarily denormalized, and TEXT was often used where VARCHAR would have been more appropriate, but still.
I am an old-school developer with a computer engineering degree but many of the old famous devs were self taught. Yes, if you learn how to code through online courses you will miss some important fundamentals but those are possible to learn later and I know several people who have.