I had both Yashicamat 124G and Rolleiflex TLRs (several of the latter, various different models from a 1949 Rolleiflex Automat to a 1978 Rolleiflex 3.5F Whiteface).
I agree that the Yashicamat 124G with the four element Yashinon was roughly the equivalent of a Rolleiflex with Zeiss Tessar aside from build qualities and feel, but do be aware that the last series of the Yashicamat changed out the four element Yashinon lens for a three element version (in essence, in Zeiss terms, changing the Tessar for a Triotar) and performance suffered. Rolleiflex models with a Zeiss Planar or Schneider Xenotar, however, were substantively better performers than the models with Tessar (and by extension, Yashicamats with Yashinon) lenses.
Regards Rolleiflex TLR services, I've always used Harry Fleenor (Oceanside Camera Repair (310) 374-6506) in Manhattan Beach, CA. He's always done an excellent job with anything Rollei.
G