"Now live with your bad/good design patterns on your own for the life cycle of your product or service, you get none of the shared knowledge and advancement through the k8s community or platform,"
This is an interesting argument, but it does suppose that the 'community' always comes up with the best solution to a given problem. A good look at standardisation processes over the years shows it can just produce the least worse one that works.
How do you avoid the echo chamber effect? People doing things because others did them before, then that becoming the 'way'? (You see this a lot with thinks like Stack Overflow... there's many cut and pasted examples of things where a few vestigial config options, or code lines have crept in as the cut and paste cycle continues, or all the websites that happily tell you the rules to drastically reduce the brute force attack space on their passwords.
Personally, I always find the companies that do things differently to be a bit more interesting. So long as you can give well thought out reasons, it often shows you've considered the problem deeper than just getting the off the shelf solution. Sometimes that can allow you to provide the differentiation between your competitors.
Mind you, get it wrong, and you'll just be re-inventing the wheel a lot. :D