A2Z
A2OC Donor
I agree with your post except the last paragraph as 185/50/16 tyre size (which was the most used tyre size on an A2) wasn't used on any other VAG models that I'm aware of and in fact are such an expensive tyre size to buy as they were only used on a couple of other cars at all one of which was the Nissan Micra.If you look at winter rally cars, you will find narrower tyres are used. So, your worry is not needed. Too wide tyres for light car is no good either.
Modern tyres are using softer compounds as well as better tread design. A2 weigh about same as mk1 Suzuki Swift Gti I used to own. Gti did have 165 tyre and it glue to the road very well.
A2 only used bigger tyres as VAG was doing cost saving by buying same size tyres for many of their line ups!
I think larger wheel tyre sizes were used on the A2 purely for marketing purposes and aesthetics, to sell more cars as they look better with bigger wheels. They don't drive better though. I personally think an A2 on the factory lightweight 15's rides the best of any wheel/tyre combinations but possibly at the expense of aesthetics