One of the big issues is that if you want an elevated position in a building, you have to deploy on the window seal.
In RO1, you could sometimes find an object to deploy on further back into the room. This is nearly impossible in RO2, I saw a table sitting by itself in the middle of a room and I tried to deploy on it just to see if I could. "Cannot deploy here" pops up. Uh? It's a table, just as big as any stacked sandbags in the game. Why are they handcuffing us?
Also in RO1 you could deploy the MG on a window without going right up to the window. This allowed you to stay further back. But now you have to run all the way up to the window and have your barrel stick out just to deploy (something that is a big no no for MGers in RO1)
So in summary, if you wanted to deploy in a window, you get to stick out like a sore radioactive thumb. Add in the fact that every player is now a world class sharpshooter and you've got MGs being nearly useless.