The meaning is definitely "(the task) is getting easier". The subject is "הקושי" and "יורד" is a participle.
It might be slightly less ambiguous in English as "the difficulty is decreasing", or "the difficulty is diminishing", both of which have narrower, less transitive interpretations.
I'm not clear what this means. Does it mean that it is becoming less difficult? If so, I would say something in English like "the difficulty level is going down" or "it is becoming less difficult." The translation shown, by itself, would mean to be that "going down" is the difficulty; i.e., it's hard to go down.
This is not an idiom or something. The meaning here is unclear without any context.
'The difficulty is decreasing' would be the more natural way to say this in English.