How can LOS's security be somewhat close to GOS if it's worse than OEM? LOS lacks verified boot, hardware security features, it's often behind is security patches.. With "advanced protection" enabled stock OEMs are even more secure, but GOS is even more secure still. When it comes to EOL devices, LOS may be more secure than OEM depending on your threat model.
It very much depends on your personal threat model, if you expect targeted attacks LOS doesn't hold a candle to GOS, but at least for my threat model verified boot and hardware security features outside of my control don't have a substantial security benefit.
Obviously it would be preferable to have up to date security patches, but as long as there are plenty oven even more easily exploitable devices, and there is no WannaCry level attack ongoing it is a risk I'm willing to accept for more user freedom.
https://eylenburg.github.io/android_comparison.htm