I can't agree more. The above shot is a mushroom, about 1/2 inch in diameter which I captured on Efke 25 with my SL66 and the 50/4 Distagon HFT lens in the reversed position.
I will say this - medium format macros are not for the feint-hearted. You have next to no depth of field available and limited (SL66) or no movements. In the field, you find yourself stopping down even more than with 35mm, meaning subject movement is often a problem. In summary, your technique has to be absolutely perfect to pull it off.