the refresh rate is just as important. Canon - 120fps. Nikon - only 60... I'd like even more to be honest.
Interesting that you mentioned film SLRs. My very brief encounter only involved 3 canon models. EOS 5 form factor was pretty much identical to 5D series, only made of cheaper plastics. T90 - actually a fraction bigger with built in minigrip - kind of in between 1D and 5D. Going back even further there was A-1, with hefty steel? body. Form factor was smaller and very very uncomfortable but there was an all encompassing huge grip that I'm sure most pros bought, not only for comfort but also the obligatory motor drive. From memory it was both larger and heavier than old 1DsII (much heavier than 1DX) in that configuration. Nikon F series I think had similar dimensions. I am not sure what else was out there, but I think it was either function or small form factor - never both. We have come a long forward way since then.
Sony is clearly moving back towards larger form factor since A7 mk1. Panasonic is quite hefty and even Canons are somewhere in between which probably makes Z6 & Z7 some of the smallest full frame cameras on the market. The mk1s aren't even compatible with grip. Luckily the ii are. I don't know if it helps much, but then there is pretty much no choice. Hopefully the market will do its thing and we will have a broader range of sizes to choose even within each brand.
I think the only reason why 1Dx / D6 are not as popular is purely down to cost, and secondarily the low-ish res sensor. The form factor is far superior to ordinary gripped SLR, making them smaller, lighter and more durable. The grips just never attach cleanly and leave a lot to be desired. I owned one for 6 years and just sold it with less than 24 hours of use.