And the entire purpose of this new subsystem is so we don't use the term "sub-species"?
Part of the problem is that WotC has been inconsistent with its own language and design. (Surprise!)
Prior to Tasha, the language was race and subrace. In Tasha, they used the term lineage (as in custom lineage) but kept race/subrace. Then Van Richten's introduced three "races" that had the extra benefit of being able to be gained later (dhampir, hexblood, reborn) and called those lineages too. Then MotM came as and removed subraces from aasimar, genasi, shifter, etc making some of the choices inherent to the race (aasimar celestial legacy) or making them completely different races (air genasi, fire genasi, etc). All the new subraces that were part of PHB races (deep gnome, eladrin, duergar) became full standalone races with a "counts as an X" on it's type.
Now 2024 is coming and screwing up that design by saying those former subraces (which up to this point were being treated like standalone races, or sometimes a racial feature) are called lineage, unrelated to the use of the world prior. Further, they have made it so a sea elf is a separate species that counts as an elf, but a drow is an elf lineage that is part of the main elf species. And a drow elf who becomes a dhampir is an elf with the drow lineage and the dhampir lineage over writing almost all of their species traits.
Ugh. Nasty language use. Sloppy design. Drow, high and wood elves should be standalone species like astral, eladrin, sea, and shadar-Kai. Lineage should be used to species who you can inherit after play (or is designed to overlay on other creatures) and legacy for choices in a species like the type of shifter traits or aasimar wing type. There is no consistency in the terminology, which is what helps fuel these arguments.