Not sure I understand why there's 4 nginx processes, 4 php-fpm processes and like 20 mysql processes, why so many, don't you need like 1 (or 4 if there' no pooling)?
That's worker threads, not processes. You can enable tree view in display options, then the worker threads would have been sorta moved to the right to indicate that fact, but that's not a default option.
Processes and threads are basically the same in Linux (except threads share resources, since we're talking about the same mysql "program" is a given that these are 'threads', sorry if I'm imprecise and call everything the same).
I'm no mysql expert but I highly doubt you need more than a few threads (a bunch for the db housekeeping and one per connection), looks like this server is not using pooling. Then again I don't know much about WP and I may be talking out of my behind.
