Yes, that's kind of the point - we're not saying that the new UI is worse, we really are saying that without a good reason/benefit, we don't like any change at all.
By default, changing the expected behavior is bad, there needs to be some benefit that justifies the change. It's not silly stubborness, it's pointing out that it is harmful and counterproductive to disrupt people's workflow. Variety is nice in food and entertainment, but in productive workflow predictability, reliability and lack of variety are very, very valuable. Saying "the new UI isn't worse" is not sufficient - is the new interface significantly better? Was the change required to enable something that I want which wasn't possible with the old interface? In that case, sure, make the changes - but not otherwise.
Every change in the interface that's not 100% backwards compatible incurs a nonzero cost, effort and inconvenience. Sure, people can and will adapt, but requiring them to adapt requires them to spend a scarce, valuable resource - attention. If a tool doesn't do the expected thing right away because it has changed, then it has failed, it has distracted the user at a time when they wanted to do something else instead of playing with the tool. That's the key difference between a toy and a tool; a toy is useful for it's own sake and should draw attention to it, while a tool is useful for doing particular things and must get out of the way, allowing the user to focus on the job or the product instead of the tool.
>"...they just don’t like any change at all. It’s silly stubbornness"
Why would I like a change in routine unless it brings major benefits? You want to annoy customers because you just feel like it? Now this is what silly is.
