Benefit of data managers: Tags for easier searching and grouping, grouping that is folder agnostic, easily choosing a thumbnail, and in text focused ones you can usually search the content of the files from one location and easily look through the results for the correct one, etc.
Different use cases.
It’s not like your uploading and downloading gigabytes to it to use ffmpeg. For that you use something local. This is for converting smaller files conveniently. For example from a laptop and you don’t want to use a public converter that might keep the content.
If you regularly convert certain file types on a computer, dedicated programs tend to be better than these combo ones anyway.