This notion that SD cards hinder performance and are slow is straight up bull and good pr. Anyone who knows even a little about computing and how an OS operates know this. In fact, it can help the speed by distributing the task between chips. It’s very simple, keep read files on your SD card and OS Apps and files on internal storage.
Basically all your music, movies, pics and documents are to be on the SD card. These are files that are rarely written to and only read (ie no slow down in OS). Another benefit is U prolong the flash memory which has a limited number of writes.
All other files shall remain on the internal memory. Basically don’t use Apps2SD. All Apps, settings and their files remain internal, close together and fastly accessible.
Doing so and my red Samsung Galaxy S3 (AOSP) with a 64gb SD card runs as fast in daily use as an S6. People complain and talk about how is just easier to remove SD cards because the average person complains after they use Apps2Sd on every app.
Well how about these easy fixes (or combination of them):
Disable Apps2Sd. Perhaps the easiest fix
Add a software warning when an SD card is detected (Simply telling the user to stick to read only files to keep the OS clean and efficient.
Add a hardware warning (same a above written on a pre inserted chip)
Block apps from writing to the external SD card. Exceptions only allowed in file managers (with huge warnings)
The idea here is simple, give your users the knowledge instead of implying they dumb and can’t learn. Btw this all is very easy to achieve since Samsung build Touch Wiz anyways.