You know you're only getting half the security updates though, yea? The Android ones you're getting, but anything in the baseband/modem/low-level hardware you're not.
Don't get me wrong, I think Lineage is great and I use it too, but I think too many people are fooling themselves on how much extra security they're getting using it.
LineageOS will be using the exact same baseband that came with Android 9 on hardware they're deploying Android 12 to, if the phone's actual support stopped at 9. Yes with the new "Play System Updates" there's better security coverage, but it's still a gap compared to supported hardware.
I had to read your comment extra carefully to realize that you weren't saying LineageOS is _behind_ on updates for the baseband/etc., but rather that it only extends availability of Android updates, not baseband updates, due to the baseband being proprietary and updates no longer being released by the OEM.
In other words, LineageOS provides the latest Android and baseband updates available; it's just that for the baseband, "latest" can be a lot older than for Android, if your phone hardware is no longer supported by the OEM.
If you get a Pixel phone and put GrapheneOS on it, you're actually ahead on OS updates compared to vanilla AOSP. For example, the webp vulnerability was backported 4 days ago, while regular Android users will have to wait until October to get a fix for this vulnerability.
(Of course, the thing about the baseband still remains, but Google now offers 5 years of security updates, which are immediately ported by GrapheneOS.)
Don't get me wrong, I think Lineage is great and I use it too, but I think too many people are fooling themselves on how much extra security they're getting using it.
LineageOS will be using the exact same baseband that came with Android 9 on hardware they're deploying Android 12 to, if the phone's actual support stopped at 9. Yes with the new "Play System Updates" there's better security coverage, but it's still a gap compared to supported hardware.