I run my own NC instance and I agree that it is slow. But at work my our company utilizes Dropbox. I am not sure if it is due to amount of files or something, but Dropbox web interface is as sluggish or even worse than my single account NC instance.

One major issue I found with Dropbox is that searching returns “something went wrong” if Dropbox is accessed through Firefox. Edge, and I presume any other chromium browsers works fine.