why are object outlines such a massive problem in HDRP? what am i missing?

I want 8 objects on a scene to have outlines when they go behind scenery. its an effect seen a million times over, even unity editor can do it.

however this seems next to impossible on HDRP without a massive performance hit.

I have purchased and tried two assets for this:

HDRP Outline | Fullscreen & Camera Effects | Unity Asset Store
Easy Performant Outline 2D | 3D (URP / HDRP and Built-in Renderer) | Fullscreen & Camera Effects | Unity Asset Store

both achieve the effect I need (EPO looks fantastic) but both cause my frame rate to drop quite a bit (from 65 to 56) when in use, even when just outlining without any obstacle masking. they are both essentially unusable for me.

they seem to use custom passes, stencils, masks, all sorts of complicated things.

is this an HDRP problem, does it have to be this way? am I missing a simple solution here.