Put em there.
Better than the intermission that 2 actually is.
So okay - further alarm and galvanize the galaxy. Great plan. There's just too much wrong with 2.
"The Reapers retreat to dark space" was part of the canon before a second or third game was planned. If the Reapers can magically appear in 2 then you fall down the rabbit hole of "why was there only one in the first game?"
The Collectors didn't "alarm or galvanize" the galaxy. Outside of Cerberus most of the galaxy didn't know/give a fukk, even less so because it was just humans disappearing. After being handed an L by humans in 1 abducting/studying them made perfect sense.
Fred.