Never realy thought about it. Most comfortable bike I rode was my Dyna Tech Quantum, 22.5" top tube and 135mm stem.
Have always bought bikes on a basis of top tube length and nothing else.
MTB: Should be x length and y angle from seat clamp centre to centre of bars.
Road Bike: Matching X and Y but to middle of a broom handle balanced on the lever hoods.
This always felt right, don't know if I am wrong or not...
Somerset, like 'Heartbeat' with newer cars!
Retro MTB: 1992 Cannondale M1000 Deore XT M730. 1992 Raleigh Dyna Tech Quantum Deore XT.
Retro Road: 1992 Eddy Merckx Corsa Extra Telekom Shimano 6500 Ultegra. 1993 Dyna Tech Ti Campagnolo Athena 8 Ergopower.
Modern: 2004 Wilier scandium Ultegra 6800. 2014 Wilier GTR Dura Ace 9000.