Do you think bike frame size is less important these days?

you obviously know this already. the key is to find out your effective top tube plus stem length. you do this by either getting fitted or trial and error. i know i need a 55-55.5 plus 120 stem for track 55.5-56.5 plus 120 for road. this gives me leeway for sensible stem length if i stick to 55.5-56.5cm effective top tubes.
it's not difficult to work this shit out.

once you know this you can tell instantly if another bike is going to fit. give or take slight changes in seat angle.

Interestingly, despite being a few inches shorter than Gary I also ride a bike with a 55-56cm effective top tube but with a 100mm stem rather than 120. The big difference is that I have long arms. :^)

However, the relationship between effective top tube length and correct bike size can vary significantly depending on the seat tube angle (steeper seat tube angle means a longer front centre for the same effective top tube length).

The way most bike companies 'measure' frames is effectively meaningless; they would be better off sticking to XS, S, M, L, XL to describe their frames and then giving the full geometry as one companie's 56 fits the same as someone elses 52.