A minor version number change in the kernel (such as 3.4.0 → 3.4.113) is not a “kernel upgrade”–it is adding bug fixes and security patches. An upgrade is moving to a new LTS such as android11-5.4 to android12-5.10, and I can’t find a single example of an Android phone making that kind of upgrade to its kernel. In fact, the Android kernels since 2020 no longer include the minor version numbers and just list the date such as android12-5.10-2022-03.
I just provided you with proof that the Fairphone 2 stayed with the 3.4 kernel for its entire existence between Dec 2015 and Mar 2023 and that Google is not upgrading the kernels in its Pixel phones. I can’t give you web links to the other manufacturers to prove that they aren’t upgrading their kernels because they aren’t publishing this information and the chipset manufacturers also don’t publish it.
You haven’t been able to point to a single Andoid phone model with an upgraded kernel and your Quora link isn’t evidence in my opinion, since it isn’t clear that the responders understand that a kernel upgrade means a new LTS. I have seen pretty good evidence from my workshop that Android phone manufacturers aren’t upgrading their kernels, but the sample of 30 phones was admittedly small and only included phone brands sold in Bolivia (which is mainly Samsung, Xiaomi, Huawei / Honor, Sony and Motorola).
In the interest of resolving this debate, we should ask everyone run uname -a on their Android devices and post their results to see if we can find any with a kernel that is newer than the year of the original release of the phone. I will start by posting new threads here and at r/purism to ask that question. Feel free to suggest any other public forum where you think I should post this question.