MCU Theory: Captain America created the Defenders timeline.
We saw the timeline Captain America created four years before Endgame.
When Marvel changed Loki’s bio they reveled that the Mind Stone, which the scepter holds, can influence people even subconsciously. In Avengers (2012) Loki used the scepter to control Hawkeye.
What if Steve used the Mind Stone on himself? The stone could have caused him to forget specific events which is why didn’t interfere in events later on.
Also, Tony retrieved the Tesseract from the 1970’s but when Steve left to return the stones he took the case they were going to but the scepter in with him.
Future Steve and past Steve both lost their shields while fighting. Future Steve blasts past Steve with the scepter. Future Steve then jumps away.
Yet the top of future Steve’s shield broke while fighting Thanos. Prior to the fight Tony said something like ‘if you keep losing these. I’m keeping the next one’ which implies that he replaced the shield Steve lost.
Since this shield broke it is unlikely that is made of Vibranium. If that is true then it gives new meaning to Sam’s line that the shield “feels like it belongs to someone else”.
What if the new timeline Steve created is the Defenders timeline? This would explain why the references to the Avengers are so vague.
The exception being the references to Captain America. The Captain America toy seen in Jessica Jones season 2 is the same one in the pilot episode of Agents of Shield in 2013. The toy looks like Captain America from Avengers (2012), which is the closest suit to the one from the 40’s except for the belt.
Jessica Jones season 3 references Captain America by name.
A guy with a hammer could refer to Beta Ray Bill, Thunderskrike aka Eric Masterson or his son Kevin Masterson, or Roger Norvell (Odin’s human adopted son).
The Nebula twist is something the Avengers should have seen coming. The Nebula from the past did not a grey robotic arm when she took the place of future Nebula.
The earthquake of the coast of Wakanda could refer to the Lemurians who are related to the Deviants a sister race of the Eternals.
The Lemurians live in the Pacific Ocean.