I strongly suspect that there's a lot more money in composer's royalties than in concert fees, for that small number of songwriters who write a significant hit song. I have no knowledge of specific numbers, but I remember Ewan MacColl ruefully commenting in about 1982 that the royalties from "The First Time Ever I Saw Your Face" were now less than half of his annual income.

Of course, I've also seen a quarterly royalty check from BMI to a well-known singer/songwriter for sixteen cents. But when a song becomes a "standard", it turns into a money machine. The extreme example was Mel Torme, who wrote "The Christmas Song" (Chestnuts roasting...). His annual royalty on that one song was in the hundreds of thousands of dollars.