I really don't think it's disingenuous. This is a very different kobold to what was presented in the 2e and 1e MM. And different from the 3e MM. I'd have to go take a look at the 4e MM, I can't remember what 4e has to say about kobolds, but, I don't recall a link to dragons. Kurtulmak is a new addition in core - it has never appeared before, only in supplements and then, IIRC, only in Greyhawk as well. What do kobolds worship in Forgotten Realms? Certainly the lore that kobolds hate gnomes because of a trick that Garl Glittergold played has never appeared in core before. And, certainly, kobolds have never been tied to Tiamat before.
So, why is it acceptable to do this in 5e but, not make similar level changes to Tieflings in 4e? After all, 4e didn't change their type - they were still demonic spawn. All that changed, really, were some basic cosmetic changes and the addition of an ancient empire that no longer exists. But that was completely unacceptable, whereas rewriting kobolds is fine.