Manchester United were a bit lucky, the whole game was possessed by Arsenal, if Arsenal attack was as strong as Liverpool then the number of goals in that match would be more numbered than yesterday score line. Arsenal had no progressive attack, they focused on one part of the field which United was aware and capable of defending themselves, a more better performance from Arsenal would have given them the winner but they were unlucky to share points when they needed it the most.
As a Manchester United fan, Manchester United is having alot of problems this period but Arsenal isn't one of it. Check history Manchester United has the most wins against Arsenal. And Manchester United knows how to play Arsenal no matter how bad inform Manchester United Players are, when it come to play Arsenal they will always be favourite to win. In the game Arsenal was very lucky to score to equalise immediately after manchester United score Arsenal responded. Manchester United was at their best in the game sharing the points at Old Trafford was a great result for Manchester United with their current squad.
Arsenal and Liverpool attacking line are not the same as you said, I know both team don't have good and reliable striker but Liverpool wingers can hurt you anything in the 18 yards.