Originally posted by rdenney 40 years ago, I viewed photographs made using a Nikon F and Nikkor 50mm lens, and a (lowly, by comparison, but still excellent) Yashica Mat-124, with its 80mm Yashinon. The medium-format image showed noticeably greater subtlety. The print wasn’t big enough to exceed either camera’s ability to make a very sharp image, and neither showed grain, but the greater tonal smoothness and subtlety was obvious.
My first MF experience was similar, a comparison of an 8x12 from Ektar 25 (Pentax MX with M series lenses) and an 8x8 from a Lubitel 166 (this was before Lomography helped brand these as 'toy' cameras). The Lubitel blew the MX away, not in sharpness, but tonal graduation. That set me off along the MF road, first a C330f, Mamiya 645, Bronica SQ and finally P6x7 (and ultimately why I bought a used 645D over a new K-1ii).
Once I started using MF, 35mm was relegated to 'snapshot' status or where MF was too big/heavy/expensive to carry. Anything of any significance went through the Mamiya 645 Pro (my pride & joy, a very expensive camera at the time). I built a reasonable system and shot everything with it. It became normal to shoot MF, very soon 35mm simply didn't cut it anymore.
With mainstream MF manufacturers there's hardly anything that's bad, poor or mediocre, most gear is very good or better and able to withstand day to day pro use. With Pentax's magnesium bodies and weather sealing it's easy to forget how fragile a lot of the '90s AF 35mm cameras were (few were cheap and many were very expensive). Spending a similar amount on used MF gear gave you a much better built camera which offered more versatility and gave better results at the expense of more weight & effort.
I prefer the weight, size and handling of MF cameras, whether it's eye or waist level shooting, exactly why I can't say. The 645D really fits in with this, a smaller, lighter mirrorless simply wouldn't interest me. I tried a Fuji G690, expecting it to be smaller/lighter than my P6x7 - it was but not enough to compensate for not being a system SLR (size is more important to me than weight and it wasn't that much smaller).