I appreciate your opinion but I disagree that its disappointed "many" fans. As mentioned Bucky taking up the Cap mantle only predates the MCU by like 1 year, so its not like there was a huge fan base behind it.
The entire MCU Civil War storyline while using bits and pieces from the comics was different, as was mentioned in the comics Cap dies after Civil War. But in the MCU he remains alive because they wanted to have him continue on into Endgame. The reason Bucky took up the mantle in the comics was because Cap dies, not because Cap hands it over to him. So of course the whole storyline of who takes up the mantle after Steve in the MCU is going to change. And in that respect they followed the comics more closely because in the comics Steve hands over the shield to Sam because of Steve's aging, which is more or less how the story played out in the MCU just slightly different.
Trust me I understand the whole thing about Bucky, as I posted on the forums at the time that I thought Bucky would take up the shield post-Endgame. But that isn't how it played out, and I'm not upset by it, and outside of internet forums I doubt many are really upset by it either. I think more they rather have had Evans remain as Cap rather than Steve handing the shield to anyone else. But that is a different conversation, and one that is likely soon to be played out as the rumors of Evans return keep getting stronger.