> GrapheneOS for instance only supports handsets for as long as Google does

Because it's not a project with a goal of breathing old life into provably less-secure hardware.

If you want to reduce e-waste, know you will be reducing your security, and use Lineage or whatever targets the most devices,

not the most security.

I don't think it's fair to say security only decreases if you install Lineage. Yes, you'll lose some security during the boot process and with debug mode, but you also get newer security patches fixing exploits your older OS would be susceptible to.

Also, my point was more: if you need to run Lineage, your phone hardware just isn't as secure as a Pixel, in multiple meaningful ways.

Could you point to a case where a fully patched Pixel, running Google Android or Graphene, has a vuln that is fixed by Lineage?

Seeing nothing but the opposite.