Seems it is a different method. Like how the monolith works differently compared to the Quantum Realm.

It fits well with what Mordo said to Strange: Playing with time can erase you from existence.

My wacky theory is that Runways and Cloak & Dagger takes place on another Earth

Since time travel worked different for the Runaways than it did in Avengers: Endgame and Agents of S.H.I.E.L.D., that might be a reason why their time travel rules weren't the same as they were in other MCU content

^No, it's just another way of time travel with different rules. Let us remember that Chase Stein used the Abstract, a book that belongs to the Gibborim that are more technologically advanced than humans, that is demonstrated when they arrived on Earth in a spaceship and this had no trace of intelligent life.

Chase Stein used the Abstract to create the quantum bracelets, does this mean that Chase Stein is smarter than Bruce Banner? No, he just had all the necessary knowledge at his fingertips to do it but that cost him several years, however if Bruce Banner had the Abstract at his disposal he could do the same in less time.

Indeed. Wasn't the same kind of deal, but it still takes place in the same universe. The Darkhold was literally in this series.