What kind of lock contention is that? (In Oracle) you'd have to be (a) manipulating the values of a primary key and (b) choosing not to index the child FK column.
Even without (b) I'd be asking "Why are you altering primary keys?" because it pretty much aint a primary key anymore if you're doing that :-)
If you've got a bit of time to spare, here's a 30min walk through of physical design in the database. https://youtu.be/x0P4zAptTiA
In this talk, we start at 10,000 transactions per second, and just by altering the design we get to 20,000 transactions per second... all on a 5 year old laptop.
And at no time did we ditch any constraints (primary or foreign). The claim that you can't get performance with constraints on a database is a myth
Anyone who says no investment has been into MySQL I suspect never took the time to read the features/release notes for MySQL 8
https://dev.mysql.com/doc/refman/8.0/en/mysql-nutshell.html