then why not buy more freighters? tha damn thing is supposed to be a TANKER, not a glorified DC-8F
Really? On what is this assertion based? Look at the USAF designations. They are KC-45 and KC-46. The C stands for cargo. Yup, these are multi-mission aircaft which include not only tanker and freight missions, but also passenger and medevac missions, along with a few more.
And about that airbus MRTT designation? The MR stands for Multi-Role and the TT stands for Tanker Transport. Once again, a multi-mission aircraft.
Given the missions USAF wants to execute with their aircraft, the KC-46 met those mission needs better.
Given the missions RAF wants to execute with thier aircraft, the A330 met those mission needs better.