I actually disagree, Kibbe said that SDs are one of the most common types.
Not every SD is going to have the same quirks as you. You do not have to have ‘long arms that come in at the waist’? to be SD. You have long arms, I don’t. I have a ‘tiny head, big body’, maybe you don’t. We both have broad hands, I’m sure there’s an SD out there that doesn’t.
Also I wouldn’t necessarily if you’re on the fence between SD and another type it’s FN. Look at Rihanna (SD-TR) and Beyoncé (SD-R). And personally I’m SD-SN, whilst presumably you’re SD-FN. These are all your personal experiences, they aren’t necessarily applicable to every SD.
And it’s because every single SD body is individual. At the end of the day it’s not about labelling yourself SD and having certain random features, it is about whether or not SD lines will suit your frame.
So if someone is between lines I recommend they try on some clothing recs and compare, instead of doing something like scrutinising their bodies to see if they have long arms or not. I understand you don’t want to see people led down the wrong way but you are also doing the same by adding to misconceptions. Personally I don’t think this post would have helped me when I was at the beginning of my Kibbe journey.