Sunderland v Manchester United

We are less of a danger on the attack without Berba
 
Naturally when you switch from 4-4-2 to 4-5-1 you'll be less of a threat.

Actually it's more to do with the opposing team chasing a goal and us deciding to sit back. Not much to do with the formation.
 
And another late "tackle".

If Bennett had done his job the match would have been over by now with an automatic 3-0 United victory due to Sunderlands 5th player getting sent off.
 
... we switched to 4-5-1 TO sit back.

Yes because it's easier to sit back with 5 in midfield than it is with 4. The formation isn't the reason why we're sitting back, the fact that we're only one goal up with Sunderland playing like they need the points is the reason.