Isn't one of the main purposes of the LineageOS project to preserve as close-to-stock of an experience as possible?
Personally in terms of security, I would worry more about the Essential-specific builds, not general LineageOS releases. For example, a quick search shows LOS having the KRACK vulnerability seemingly patched the same month after public disclosure.
As for my distinction between Essential builds vs. general LOS builds, bear in mind LOS has not reached Official status for the Essential phone and is very unlikely to within the foreseeable future, primarily due to the difficulty in decoupling Google services from the OS. BUT! If the Essential LineageOS Discord channel is any indication, maintenance and updates are super active. And, the (volunteer-run) support is VERY helpful. Keep in mind, they are supporting LineageOS on Essential, not necessarily cases of rooted devices.
Furthermore, rooting isn't a 1-click process at this time, either. You'll have to bust out the computer terminal, run some adb/fastboot commands, and do a couple additional things that get your hands dirty.
If you use T-Mobile and have the money for a Pixel 2, I would just go with that. Essential has widely varied reception for T-Mobile users. Mine for example simply doesn't work much of the time that it says I have full signal, and it flat out drops incoming calls and text messages with absolutely no indication whatsoever that anybody even tried to contact me.
I kind of regret my choice in phone to replace my aging, problematic N5.
Pretty healthy pool of LineageOS phones "out there."
https://wiki.lineageos.org/devices/