When I started to digitise our DVD/VHS collection I was running off a server, tried several pieces of software for the front end and settled for a while on UMS. Then I saw Kodi on an RPi and went down that route with an RPi3. Moved from a 1TB HDD to a 3TB to a 6TB USB HDD all on the RPi3 with no problems. Then I tried to switch to the RPi4 and I've encountered problem after problem.
There are two reasons for choosing the RPi route:
1) its small and neat (apart from the rats nest) - I have things stuck in a draw which is part of the TV stand
2) its inexpensive
So to repeat, the problems only started with the RPi4, and from my experience are more software development than hardware related (based on years of being in IT as developer, consultant, and manager). I think I came in when it was still to immature and hadn't appreciated how long the development / maturity cycle can be in the environment that Kodi/LE is developed in.
I can "solve" the problems by reverting yet again to the dual RPi3 setup and tolerate the major rats nest of cables but a single RPi4 is a much neater solution.
PS: I loved your response about the SD card speed - wish I'd used it.