I don't really think these studies show that acute blood sugar level elevation is causing the damage you are talking about. The first one talks about how TII diabetics tend to have lower β-cell count and higher apoptosis frequency, but that doesn't mean they go through waves of apoptosis more frequently (ie: during blood sugar spikes), it means that they have a lower life span. The study doesn't establish causality, so it's unclear whether diabetics have lower β-cell count because they are diabetic, or whether lower β-cell causes diabetes. It is a great study though, pretty well designed and building on kind of amazing resources from the Mayo Clinic.

The second study is interesting but extremely limited due to the fact that it was does in vitro. The problem is that it's talking about kidney fibrosis, or scarring of the kidney due to inability to regenerate. But when you remove much of the kidney and the surrounding body and then attack the kidney with glucose of course there is damage. That doesn't mean that in vivo the body can't deal with it. Kidneys do have a hard time regenerating, so it's an interesting foundational study, but I'd hardly call it "a lot of accumulating evidence."

I'll readily grant this can reasonably be construed as suggestive but not "a lot of accumulating evidence", my bad for phrasing it improperly. To me this line of research is raising interesting questions warranting further digging, in a "hm, I wasn't expecting that result going by the received wisdom" way.

Following the sporadic posts of Type 2 patients in online forums self-reporting success at getting off conventional treatment protocols, what appears to come up in common among them is what is currently considered (by the ADA and similar outfits in other nations) radically aggressive methodology to blood glucose control; <100 mg/dL post-prandial is not considered out of line in that crowd, and they avoid spikes as much as possible. A very small number have been at it for 20+ years and well into their 60-70's, and are reporting no long-term disabilities commonly associated with advanced stages of the metabolic disorder. They tend to be in very low (<50 mg/day) carb or even ultra-low (<20 mg/day) carb regimens, or constant ketosis, or varying fasting cycles, with varying amounts of exercise, or a combination of all of the above, with lot of nuances thrown in by each individual. A lot of what they practice directly goes against published large institutional guidelines, but it is really difficult to argue against the end results in their comprehensive blood panels and other bio-markers, so it is a fascinating case to me of the impact of an N=1 / DIY / Quantified Self ethos that increasingly more people are embracing with the aid of increasingly better technology. I find it really exciting that increasingly more laypeople are empirically "science'ing the shit out of this" (to paraphrase "The Martian") with a continuous hypothesis-test-adjust loop upon themselves. It is definitely not science by any conventional means, but as haphazard as it is, it is yielding in a startling number of cases exceptionally better results than the average and mean Type 2 patient experience.

I want to be clear though: there is certainly evidence that very high blood sugar causes significant damage, sometimes permanent, I'm not contesting that. How high "very high" is varies, and as far as I know doesn't really happen in people who aren't diabetic. All I'm saying is I don't think blood sugar spikes are bad for non-diabetics, but they certainly are for diabetics.