Firstly as stated already the old threat you are talking about is the previous G1 system which really is not that different from what we have now.
Secondly your entire post is completely wrong, underneath it all is still the same elo/glicko/mmr rating system that is your actual threat level. What the colours/numbers are a top of that regardless of if its the new/current/old version of threat is just a graphical representation to show a rough estimate. Going back to the old system does not actually change how matchmaking handles threat, just how it is shown to players.