Bearing in mind VHF/line of sight does it not occur to you that ATC, also being busy, might not hear them? How often do ATC ask aircraft to relay? Just because you, at FLwhatever can hear them doesn't mean everyone else can.
Almost two years ago that is precisely what happened to me (amongst other things). It took at least two if not three calls to D&D before they were able to hear me and I was only able to maintain sufficient communication with them to know I was identified. Things went from bad to worse - the radio problem meant that they could hear me but I couldn't hear them - it was like trying to listen to a conversation in a room a hundred yards away when the sound was very muffled. I knew they could hear me so kept talking and telling them what I was doing, seeing, etc. The radio volume WAS turned up to maximum. The transponder decided to join in the fun and refused to work as did the spare hand-held radio. As I turned crosswind and descended to 1,000' at what turned out to be North Weald, the radio suddenly cleared and I could hear the very welcome voice of an Emirates Airbus pilot 37,000' somewhere way out over continental Europe. A lovely, very reassuring man who really helped me enormously and whom I shall never forget. Apparently someone near Hull also tried to help but I never heard them. By the time I reached 600' I could hear D&D clearly and the last North Weald saw of me was a climbing turn out to the right on final as D&D talked me to about eight miles from Duxford which was my intended destination.
That was supposed to be my QXC.