The entire MCU doesn't count as build up for Doomsday, just like the entire Bond series doesn't count as build up for the next bond film. Or the last NFL season doesn't count as build up for this upcoming NFL season. And in IW/Endgame they had a perfect mechanism for tying the movies together (the stones/gauntlet)
The reason the MCU until Endgame was buildup for IW/Endgame is because they started dropping plot points, characters, and hinting at things along the way. They didn't do that in this phase, they couldn't. As they literally started off moving towards the Kang Dynasty story line and abandoned that. (Loki and Antman Quantumania are both prime examples of that). They have tried to pivot to make RJD's Doomsday a part for part replacement for Kang, but he's shown up as a post credit drop in a grand total of one movie.
Doomsday is the Brony to Thanos's LeBron.