[dredmorbius]

Not sufficiently in my experience.

Is this a user setting / tunable for aggressiveness?

[pxc]

There are various extensions that use the native "discard" API that is enabled by default, but give you more knobs to tweak. If you search for "discard tab" in the add-ons store, you'll find a bunch.

I use this one: https://webextension.org/listing/tab-discard.html