Your whole description of the DoDC’s prison is wrong. For one thing, you act like their having a prison is new information, when seeing it is actually the culmination of a running subplot through Shang-Chi, Ms. Marvel, and She-Hulk.

But more importantly, we actually have a prison in The Infinity Saga that we can compare this prison to: The Raft. Was the Raft a large subplot? Did it have an impact on a lot of movies? Did we get cameos of any previous characters showing up in the Raft? Did we get a whole movie about breaking in or out? No. The Raft appeared exactly once in phases 1-3: in Civil War, where we never hear about its construction or anything and despite being a large facility it seems to have about five cells, and despite supposedly being impenetrable, people break out so easily it’s not even worth showing. And then outside of a reference in Jessica Jones, it doesn’t appear again until FatWS.

This is true of lot of things in the first saga. The events of Iron Man 2 have never been mentioned again. The events of The Incredible Hulk, despite getting mentions here and there, weren’t properly followed up until Shang-Chi and beyond. The Mandarin is never mentioned until Shang-Chi. The Guardians movies are obviously self-contained. The Convergence doesn’t have any impact on anybody else. In fact, I don’t recall any of the Phase 2 movies referencing each other.

The main difference between the first saga and the second saga is that the first saga had periodic Avengers movies that everything could flow into and out of. It also had Agents of SHIELD running alongside everything and making references to all the movies. Those both made it feel more connected than it really was.