I am 6'4" (193 cm) and 240 lbs (108 kg). A big boy. I require supplementation at 5000IU to maintain ~48 ng/mL, which is just about normal.

It is impossible, at my latitude, to obtain adequate exposure to sunlight. I tried that.

My doctor said "hmmmm your vitamin d is 9... maybe that explains the all-appendage tendonitis and muscle soreness" and recommended supplementation. I really like being able to spend 10¢ per day on D3 and K2 from Amazon instead of paying for 200,000 IU injections every month or two.

You missed their 10,000 IU: https://www.naturemade.com/products/vitamin-d3-maximum-stren...

The audacity to believe you know everything about this subject.

Super-high dosages are used in loading protocols before switching to a smaller maintenance dosage.

It didn't sound like arrogance to me. The "if" at the start of the sentence indicates they are not asserting their conclusion as the only truth. That said, if toxicity is a large concern, it's strange that companies sell such high dosages at least without some kind of warning. I bet a sufficient warning would prevent at least some cases of toxicity

A lot of OTC medications have potential issues and interactions. That said, my primary care recommended I take vitamin D based on blood work and no one has batted an eye at my taking 5K IU. So the idea that's some widely-accepted radically dangerous dose is simply untrue. (Doesn't mean it's a wrong idea but it's not one that doctors generally accept.)