I believe in the "old" matchmaking system (before the introduction of rate, epic and legendary items) the matchmaking was spaced out such that base "rare" (currently legendary) torsos would not be matched up - e.g., level 28 would not be matched up against the next "legendary" (rare) torso which was level 32 and so on, level 32 would not be matched up with level 38, level 38 was not matched up level 45 and so on. We need something like this in order for the battles to be competitive.
The matchmaking does not to be fixed to a certain level, however I believe it needs to be spaced out between the legendary builds.
But I think they wanted to do, because there is 4 level difference between the legendary torsos. But now the level difference is 5. And the fusion core turned everything upside down. So I think they are on the case, just have not been able to reconcile things.