From all of those, Metagross seems to me the most useful one to buy 2nd move. I’ve run it for some time just with MM (dust issue) and it was not nearly as good until I bought it Earthquake. Depends on its role and how it’s positioned in your team, but as my go-to steel type, it’s the only move that really hurts fellow steel tanks like Dialga or Heatran.
Funnily, I’ve run hundo Dragonite with just that DB/DC and I feel it’s not lacking a 2nd move, at least not from within its current move pool. If it had something added that can really hurt Togekiss, steels or rock users, I’d buy it NOW (just imagine Icy Wind or Superpower for a second… yeah, I’d buy that).