It is easy to note that the Michelin XAS and the Pirelli Cinturato win the appearance competition, that is easy. they are both buil, with genuine period tread patterns.
However it is the drive of the car that makes the real case for buying period tyre carcasses that are built to be fitted to a classic car chassis. Yep the Dunlop Sport Classic and the Vredestein Sprint Classic are not bad tyres but they won't handle as nicely on your classic Alfa as a genuine period tyre, and they aren't genuine classic tyres and they don't look right. nobody is really going to look at either of those tyres and say they look classic, because they do not have a classic tread pattern and it has the word "Classic" written on the side wall. For me they would have to be loads cheaper to consider them, but even then i wouldn't.
However a tyre such as Vredestein Sportrac will keep your rims off the road, but they will never drive as well on an Alfa Spider as the Cinturato or XAS. they are built for another kind of car altogether . I do not think you should choose your tyres just based on price, which is the only reason to buy them. no doubt they won't handle as well as a Cinturato or XAS does on a '60s, '70s chassis design. No doubt they look totally wrong. And wouldn't people be happy to spend more money on buying a premium brand tyre such as Pirelli and Michelin. I actually don't think the Cinturato's are expensive.
I think there are loads of Alfa in the UK fitting the Cinturato 185/70VR14 CN36. we can't have sold them all to MGB owners. They pretty much only fit Alfa or MGB. If you look around Alfa BB forums you will find lots of people who have fitted them, and all i ever here is praise. Has anyone fitted the Cinturato and not liked them?
I think the perception is that modern tyres are better because of the developments over the years
Carcass designs only benefit you if you put that tyre on a modern car chassis.
Modern compounds - Well these classic tyres are using modern compound, and they are even better, because they are Pirelli and Michelin compounds
Tread design - yep fair to say modern tread designs are better at being quieter, and yes they do move water better, but you are only really going to aquaplane if you start fitting over sized tyres.
The only 2 things that makes a modern tyre attractive on a classic Alfa
1/ if you have completely modified the car changing caster, Camber, Springs and Dampers, ie unpleasant ride and handling on the road but loads of grip on the track
2/ because they are cheap.