it's great to know that Sublayer LOP supports .abc and that this is the preferred way of importing it
I think the source of confusion is partially due to lack of information about what filetypes Sublayer LOP supports
most of accessible doccummentation deals with .usd file types and in LOP help tutorials you import .obj files through SOPs even though Sublayer SOP supports .obj too
so maybe more training material dealing directly with Sublayer LOP for importing various filetypes would be helpful
or at least the File Browser in Sublayer and Reference LOPs can have supported file type filters instead of just * (even though not sure if this is possible to be dynamic based on which file format plugins are currently installed)
WRT to Sublayer supporting a format, it actually supports any format USD is aware of. In Houdini any geometry format supported by Houdini can be referenced/sublayered into LOPs; SideFX has USD format plugins for all their geometry, which is super cool (you can sublayer an obj file directly, see screenshot), though you don't have a lot of control as most of these formats import into USD suboptimally (Alembic, and probably bgeos+packed prims, being an exception).
I try too look at this support as temporary convenience for converting data into USD for 2 big reasons:
- Only a USD library that has SideFX's plugins will be able to read those non-USD layers
- Even with a file format plugin, non-USD formats will not perform as well as USD
Alembic files are a bit of an exception to #1, since that plugin ships with USD and convert pretty well to USD. However, it still has the performance hit in #2. For more info, see https://graphics.pixar.com/usd/docs/Alembic-USD-Plugin.html#AlembicUSDPlugin-KnownLimitations
Hope that helps!