We negotiatied with the Haaland camp in December 2019 until he decided to sign for Dortmund around the 25th that month. (He has said many times since that he signed for Dortmund because he felt only the manager and not the club wanted him here, he was not guaranteed minutes and we didn't include a release clause in his contract.)
Greenwood had at the time Haaland signed for Dortmund started his first PL match (plenty of short sub-cameos though) and started some games in the EFL Cup and EL (goals against Rochdale, Astana, Partizan, AZ (2) and Sheffield U in around 1000 minutes). There was reason to believe Greenwood was a good talent, but there was no reason to believe Greenwood was close to Haaland levels (28 goals and 7 assists in 1464 minutes - 8 goals in 374 minutes in the CL so far that season). The argument that we didn't need Haaland because we had Greenwood was just silly.
Not as silly as the "we don't need Bellingham because we have Mainoo", but I guess you get my point.
If you have a chance of signing the next superstar in a position at 19, you do whatever it takes to get him, even if it makes the road from the academy to our first team a little bit longer for some of our talents.
I don't think we'll get Bellingham, but he would be a fantastic signing for us, even at 100M+....