Up to now only some concept art was published. I think the offer of SpaceX (or any other competior) was not disclosed - correct me, if I am wrong.
When looking back to the first pictures of the Mars Colonial Transport, that became BFR and then Starship, this changed quite a lot in size and performance. On the other hand, Starship is already flying, so the cornerstones of its design are determined. Still, all this on-orbit tanking is a far way to go, and reducing the number of tanker flights may be worth to improve mission reliability.
When looking back to the first pictures of the Mars Colonial Transport, that became BFR and then Starship, this changed quite a lot in size and performance. On the other hand, Starship is already flying, so the cornerstones of its design are determined. Still, all this on-orbit tanking is a far way to go, and reducing the number of tanker flights may be worth to improve mission reliability.