It looked quite innocuous, but that's only because Nani ducked out of the tackle to ride it, if Nani challenged for the ball he was in big trouble. It's silly to dismiss it as not being a red, the laws say excessive force is a red card, and the ref judged it as that, quite understandably.
The problem is just that, he didn't duck out of the challenge, Kompany was simply on the floor before Nani got there, it wasn't studs up in the way that "studs up" means dangerous, 70-80% of tackles are "studs up" literally, studs up generally means in a dangerous way and usually high, his were neither.
THe vast majority of tackles in between standing and sliding on the floor 2 feet are off the ground, 2 feet are off the ground when you run, so if you tackle as you run it would literally at some point be a "two footed challenge".
The danger, recklessness and red cardable part of it is if you don't hit the floor before you get to the player, so you're still mid air with your studs/feet above ground height AS you reach the player, that is when a tackle moves from on the ground to a leg breaker.
Had Nani had contact made, it would be from likely one foot, on his foot, not high and no more dangerous than most tackles.
Also two footed is, difficult, in terms of a stamping motion its when you jump in on a player(after the player gets there) with both feet together. Also what makes a tackle particularly dangerous is if the legs are locked straight because both its much harder to pull your legs away and there is no cushioning in the contact that happens when the legs are bent.
Kompany was, on the ground before Nani got there, got the ball, not sure he even touched Nani, his feet weren't that close, nor were his legs locked out.
Sorry but, its not a foul, not a yellow and not a red.
Entertaining game though, but City spent too much time defending and peeing around in their own half when they could have been attacking.
Mancini is making the same mistakes he's been making all year, generally speaking in the big games Silva has been anonymous and Nasri has been useless. Those two together just isn't a tough team, nor a hard working team, nor a good combination.
Considering the back line you could almost without question expect, Evra, Rio, Smalling, Jones, they put three midgets out, two of which have looked poor recently and poor in these types of games. De Jong also started off pretty poorly but grew into the game, he looked very out of form and not really match fit. But got better as time moved on, again had there been a bit more rotation up till now City would likely have less injuries AND their "back up" players would have a little form to carry into games like today.
Johnson didn't look fantastic or anything, but looked a damn site better than Silva or Nasri in effectiveness, and is obviously way faster than either which was something they would clearly need to break more effectively.
Basically I think Mancini got almost everything wrong.
Jones though, bad crossing, bad passing, bad tackling, was generally just woeful. Looking less and less like a out and out defender each time I see him.