The important question - Were they any better than modern guitars (Not just gibsons, but by any company)????????
On average the old Les Pauls (the '58, '59, '60, '60 Black beauty, '52 trapeze, and '59 Les Paul Juniors I have tried out so far) are all built with a little extra attention than many Gibsons of the Norlin era and part of the current era. They are very nice guitars and made special due to their rarity and when they came out in the early days of rock and roll and how they influenced a whole generation. But no, they are not that much different and certainly not "better" than the reissue line Gibson has now.
The custom shop stuff has the benefit of clean wiring and absolutely no fret or fingerboard wear. You can get a used '59 reissue for around four grand to start with and it's certainly better than spending $100-$500K for a real '59 flame top.
As for other companies, Gibson and the old flame tops fall in the middle somewhere. They are definitely better than an affordable Squier, PRS SE, Ibanez GIO, or most sub-$500 dollar guitars. But they are not any better than most American Fenders, Ibanez Premiums, Gibson Les Paul Standards, or similar $500-$1500 dollar guitars. And honestly, they don't even get close to an Ibanez J Custom, Anderson, PRS McCarty, or ESP Custom Shop.
What people pay for is the history and the rarity of these things. If I had absolutely no knowledge of history or worth, I would easily take a Gibson Slash reissue with AAAA flame and custom pickups over an old 1959 Les Paul Model with a faded flame top and scratches everywhere.
The collectible and rarity thing is the same reason a person here would pay eight grand for the Jem EVO over a perfectly brand new Jem for far, far less.