I don’t really see Spa as being all that different. Lots of elevation, mix of high and low(er) speed corners, so fairly similar. Nordschleife has lots more corners, and is bumpier, but the big difference is the length (and number of corners). A small bobble in a single corner & you’ve blown your lap. Those bumps at the Nordschleife make it so much easier to make a mistake, and all those corners give so many more opportunities for mistakes+ any one mistake will kill your lap… So, times at Nordschleife tend to favor cars that are really fast, but reliably so (or at least have big enough pocketbooks to give them enough chances at a good lap). There are some cars that are insanely fast, but more difficult to drive absolutely at the limit. They will be very hard to set a solid laptime with… it’s also rather expensive to have the ring all to yourself to go for that perfect lap, so it’s not like you get all that many attempts at it (unless you have that nice pocketbook behind you of course)

So … I don’t think Nürburgring lap times are a great metric, but I do think they are a better metric than you’d get from lap times on a similar, but shorter, circuit. (Source: I have laptimes at Spa that I’m fairly happy with, but have yet to set a single lap at Nordschleife that I’d say is great, but Harry’s Lap Timer says I have an optimal lap to be proud of)