And except for the absence of the Illusive Man they were EXACTLY that in Mass Effect 1. That is, to the extent that you could tell any two missions apart, but that's Mass Effect for you.
No it's not. All we saw of Cerberus is a handful of VERY SMALL outposts scattered over a few isolated planets.
Which, as I said, is about as much as we saw of anything
in ME1. The same battle map slightly redecorated stands for a Cerberus facility, a Geth fortress, a crime boss' headquarters and an illegal ExoGeni lab.
ALL the side missions were this way; Shepard could have knocked over Fort Knox and it would exactly like the underground bunkers on Luna.
In ME2 & 3 we see them with at least large space stations, one of which is equipped with drydock facilities, several VERY LARGE and purpose built facilities with their logo slapped on just about every wall and door. In terms of assets and manpower it's several orders of magnitude greater.
Again, much like everything else
in the Mass Effect universe. Even the side missions
in ME2 are better developed; the stranded freighters you keep boarding are suspiciously large for vessels that are supposed to have only one level.
Imagine if they'd done ME3 the same way they did ME1. The Noveria fighter base would look exactly like the Cerberus reaper lab, except the fighter base has this one room with a door on the ceiling and some fighters lying around and the reaper lab has some generic alien artifact in the middle of it.