I think they are spelling it out.
In Avengers someone else might well have sent Loki. He was working for someone else after all. Plus he kept talking about "knowledge gained" from "others".
Using the Tesseract back them was not easy-use plug-and-play teleportation. It opened
wormholes which people could pass through in Avengers and even then a big contraption was needed to keep the hole open for the Chitauri.
It was early days and all but 2021 Tesseract usage suggests that Loki could have just teleported his team around the planet (rather than Fly for example) and that the Chitauri could have been (at least piecemeal) teleported to Earth.
When Shield were chasing Loki and Hawkeye,
2021's Loki could have just teleported him and Hawkeye away. No need for an elaborate chase with the risk of being caught.
I am just saying that they have now underlined its ability as a
personal teleportation device and that was not as clear in Avengers I.
Anyway it's just am idea and probably wrong.
@AnonymityX1000