Mainstream = lowest common denominator. Don’t try to impress me with your lists of mainstream bozos, point me to an undiscovered talent out of the left field. Spare me your Woodstock taste.
With exceptions, mainstream sucks.
IMHO, there isn’t a singer I’ve heard that can compare with Czeslaw Niemen.
He was a bit Proggy and Pretentious at times, but his vocals literally could bring tears to my eyes.