You dont understand the argument. One of the two pilots should always be someone with some basic time flying the airplane. The check airmen are ones getting this training in the actual airplane. That way while they teach new CPs from the right seat its not new for both with folks in the back. This is not an FO argument, as the captains should have flown and logged several trips before the FOs get off IOE to avoid green on green. And yes, when UA gets a new type they fly it outside the sim part 91 too.