I really don’t think that’s the case at all.
If we’re looking at the different jobs involved with getting music into my ears and assume all people are at least good at what they do then a good composition will likely take far longer to write than record. For orchestral music, or “classical”, then writing takes a fair amount of time whereas for a recording what you need is a good orchestra, room and engineer and then you’re done. Can take weeks to write and you’re done recording it in a day.
For popular music it’s obviously a bit different, but since not everyone is a Lennon / McCartney we’re still looking at a fair amount of time for songwriting and less than a day to record.
Now, obviously, if we want to get into the weeds of production and do a ton of musical sound design etc then yeah, it’ll take longer.
But I think that’s why it’s not entirely an impossible apples and oranges comparison. What would they have done? Well, if we had a time machine and allowed them to create faster then I think it would have been very interesting and they surely had output more and-or different music. On the other hand, if we had gone back in time and brought them back to our time and raised them here from their youth then I think it’d have been very different.
On average things are very different now as we behave different when creating art and relating to art as consumers.