Just letting you know that SBMM is not in Iron Banner. What you are seeing is CBMM. SBMM has only been added to the Control playlist and Bungie are actively monitoring it and will make tweaks to it until they are satisfied that they have an optimal solution. In other words expect it to evolve over time. Some in the community are hell bent on getting rid of it but IMO their efforts are in vein as Bungie has quite clearly spelt out their long term objectives for PVP and SBMM is front and centre as part of it.