I'm with you mountainsunsets - although I recognise this can be very regional. If I lived in rural Wales and had vet's bills like my friend's, who seems to pay c.50% for a similar condition, I might not bother insuring. Here in the South East ... insurance is a must!
Each to their own of course, and some people might prefer to have a 0% credit card to hand for back-up, but it needs to be a well throught-through decision rather than just looking at the headline of having a few thousand in savings at the end of the year if you've not needed to claim.
Even GSD20's £3.5k per year would not begin to touch the sides of any reasonably significant vet's bill. A neighbour recently rescued a dog, and within two weeks it had chased a deer and been hit by a car, and they were in hock for £8k - and what if two dogs needed that in one year? The logic of insurance being expensive because the dogs are large also means the vet's bill will be larger, as so much dependent on weight.
I (touch wood) have healthy breeds, but none of that stops e.g. an accident/injury, or illness through eating something they shouldn't on a walk.
Obviously some people can afford to 'self insure' and it's of no consequence what the final bill might be. I would rather know I have at least a good amount of insurance cover and can make decisions based on what's best for the dog, rather than what I can afford in a crisis.