Yep, of course like I said it's an oversimplification because dialect continuums are tricky to measure, but if a Berliner and a Viennese tried speaking to each other in their local dialects they likely wouldn't be able to understand each other and would have to switch to Hochdeutch (best case scenario) or English (worst case scenario). There are also amusing stories from northern Germans I've heard getting so lost in Bavaria they started speaking English instead lol.

So yeah I agree, even when the East-West divide starts to be reduced I'd bet Austrians will still stay better at English than Germans.