Speaking for myself of ffmpeg and imagemagick, I don't find the CLI itself difficult, I find that their application domain is a bit complicated for a layman.
Meaning I usually struggle to comprehend what particular options mean rather than how they bind to CLI.
Maybe indeed a good intuitive UI would give more intuition about the more obscure options. But then again, a good intuitive UI is a quest of its own.
Merge a separate video and audio file without looking it up - I've got a document stored that lists all the different commands I've used and hopefully some context about what they do.
What is difficult with ffmpeg is the sub-language in each argument, which depends on the filter you’re using. I can learn to lookup the manual, but if I have to go to the internet to learn the syntax of the filter, I’m better off googling my usecas.
And using multiple filters in one call is even more funny. Getting the output and parse it too, as it can be different in different versions and it's terribly inconsistent between filters.
Meaning I usually struggle to comprehend what particular options mean rather than how they bind to CLI.
Maybe indeed a good intuitive UI would give more intuition about the more obscure options. But then again, a good intuitive UI is a quest of its own.