Warrantywise does aftermarket extended warranties in the UK.

I can't say how but it seems to me that may have an influence on their data.

They do include the cost to repair among other things, which means that only do they break often, they also cost a lot to fix. Cheap brands on the other hand when they do break down are either fixed by the manufacturer for free or dont break as often. German cars are infamous for the high number of defects that their manufacturers wont issue recalls for. Therefore the ranking is accurate.

It still feels a bit off. I expect an expensive car to have expensive repairs. When looking at the cost of a repair I would perhaps consider the cost as a proportion of the MSRP, or resale value, not the raw cost.