I do love thought experiments like this but do believe they’re insatiably unresolvable.
The old BBC Connections series has a segment with James Burke using the old census tabulators.
thus CD runtime was derived from something "what we had at the time".
The 74 minute length resulted from Sony rejecting the Philips 60 minute 11.5cm diameter “Pinkeltje” disc size in favor of a 12cm diameter.
It’s quite possible that Sony’s Norio Ohga simply argued that the 9th symphony or various operas fitting would be enough of an advantage for the slight size increase without meaningfully decreasing portability.
The symphony story might be a legend, but it's pretty well known that the original design was somewhere in 10-11cm range, but this was eventually increased to 12 cm.
The "diagonal cassette size" seems extremely far-fetched - first, who cares about this? If you are worried about boxes, shelves etc.. you want horizontal size, which 10 cm. And you are worried about holding in hand, 12cm is not very convenient for the smaller hands, a smaller size would be better.
That said, I doubt that's the reality either... it's probably a number of factors. I am slightly surprised that a USB based read-only media format standard for players hasn't materialized, though it seems that online/rental models are what the industry really wants.
>The disk diameter is a very basic parameter, because it relates to playing time. All parameters then have to be traded off to optimise playing time and reliability. The decision was made by the top brass of Philips. 'Compact Cassette was a great success', they said, 'we don't think CD should be much larger'.
>As it was, we made CD 0.5 cm larger yielding 12 cm. (There were all sorts of stories about it having something to do with the length of Beethoven's 9th Symphony and so on, but you should not believe them.)
> The 8-14 bit channel code was agreed and all the specifications between them led to a playing time of 75 minutes.
Something related to the width of a two-horse Roman carriage… Not sure ;-)