It depends on if you want rank to be an accurate representation of player skill, or if you want rank to be a kind of progression system.
If you want it to be purely a representation of player skill, then players ought to be able to place Onyx. The current system is black magic voodoo levels of good at approximating player skill in just a couple games. It only took 3 or 4 of my placement games before I was matching consistently with players in Diamond (nobody had gotten up to Onyx in the first day or two). It doesn’t make any sense that the system can know immediately that a player belongs in Onyx, but then forces them to grind through Diamond anyway.
I don’t like the old grind based ranking systems of Halo 2 or Halo 3. There’s no point dumping everyone into Gold even if they are obviously Platinum / Diamond / Onyx players… it will just frustrate everyone.