You're very active! Even so, I wouldn't think the IF itself was the problem, probably you were having trouble eating enough for your level of activity with such a regimen.
About bloodwork, I believe you're mistakingly conflating insulin and blood sugar. Blood sugar may vary in such a way, but it's just a proxy because insulin is so hard to measure.
But more to the point, I wasn't referring to intermittent fasting solely, I believe even longer fasting periods are required. Regardless, even IF is a far cry from what the average person does.
I also disagree that fasting is not a panacea. It's a close to one as we have. I don't think this is a subject I'm likely to convince skeptics in a comment, so I will simply say interested people will find reputable resources on the subject, including striking anecdotes published by fasting clinics (of which, for some reason, Germany has a few that publish material on YouTube).
Autophagy doesn't really kick in until 2-3 days of fasting.
Someone tells me they're fasting, I don't expect they mean 8 non-contiguous waking hours without eating (with sleep in the middle). That's, like... pretty close to a normal day. It's easy to have 16 hour "fasts" just by accident. "I only ate two meals yesterday because I was fasting". LOL WUT? Again, I know, technically true, but not a useful way to refer to it, IMO.
I've switched over the last 6 months to eating 3 meals and 2 snacks a day of varying size. I climb often (vigorously, 4 times a week if not more) and found that fasting was simply insufficient to provide the energy I needed. IF caused notable performance decreases at the level I work at leading to more injuries due to poorer recovery. Changing my diet in this way fixed most of it. Of course, I try to eat relatively clean (but chips are a weakness). I don't have a 6 pack but I am also not overweight and carry enough muscle for my uses.
This isn't to say I am giving a license to eat what you want. But what you do with your fuel is probably just as important as what that fuel is. The "average person" you mention is a couch potato. Of course these people not only benefit from IF but literally any change in exercise! IF works great for people who are not intensely active. Hence why it has become popular in tech. Proper sleep (whatever that means to your body) and relatively hard exercise are even better predictors of all-cause mortality than any of this. To me, after having done it, IF feels mostly like new age woo-woo "science" and it dances around people saying it flat out cures cancer. In some cases, for example prediabetes and chemotherapy, "deloading" the system has evidence of being effective. For the rest of us, it's a wash.