Not sure why you had confusion on RNAV or Loc/dme? We norm offer the RNAV them Loc/dme if people cannot accept RNAV. As for the decent to 2000ft this is the start level for the procedure and ALL of the local operators ask for decent to 2A for the procedure! Plus the controller may have needed the vertical separation again preceding or other traffic in TMA.
I didn't say "confusion", I said "frustration".
Nor did I mention Loc/Dme. The ILS was notammed as u/s but we were offered it ,and cleared for it too.
2000' is NOT the "start level" - there is no such thing.
I cannot explain why "ALL" the local operators would ask for descent to 2000' as this makes flying a continuous descent more tricky. Maybe they are choosing to fly level at 2000' and intercepting the 3deg approach path.
We prefer to stay at 3deg descent all the way as it's more fuel and noise friendly.
Your last comment is a little worrying. If we are cleared for the RNAV then - by definition - we are cleared all the way to the MDA. So to the include a descent limit point makes the clearance invalid. If you want to have the possibility of clearing other a/c below the RNAV then all you need to do is include minimum heights on the procedure.
But (if you understood the principal of RNAVs) a/c will be on the 3deg approach path after the FAF!