Apropos geometry...fashion has had a role to play here, but notwithstanding that, you'll see if you take a look a frame styles through the decades. From the late 1940s to say the mid 1990s (effectively the demise of the pro steel raceframe) that geometry, clearances etc have changed over time.
Stage race geometry, one day race/criterium geometry, time trail geometry, track geometry - all different down the decades.
Only you can decide whether the fleabay bike is a good buy.
Co-founder of a V-CC section, member South Eastern Road Club and owner of - 2005 Bianchi Reparto Corse (modern), 1985 Raleigh SBDU Pro Super, 1984 Raleigh LU Corsa, 1980 Allin Stan Butler Special, 1978 Ron Cooper, 1975 Bill Philbrook tourer, 2 x very early Roberts (mid/late 1960s), 1966 Raleigh Superbe Roadster, 1964 Allin Stan Butler Special Belgique, 1951 Hobbs of Barbican S/C, 1950 Hobbs of Barbican S/C, 1947 Hetchins Super Special, 1908 Centaur Featherweight. 1988 Specialized Stumpjumper.