Collins dictionary disagrees:

https://www.collinsdictionary.com/dictionary/english-thesaur...

and

https://www.collinsdictionary.com/dictionary/english-thesaur...

They are each their others 2nd top synonyms

I agree that the spectrum of "effort needed" is not the same as "clarity of process", and ideally people wouldn't blur the lines... But it happens anyway.

For example: Moving a heavy exercise-weight one mile in a straight line through an open field field is very straightforward... but not necessarily easy.