I don't think today - and to some extent, quite a few games in the last month or two - should be much of a surprise. We bought him at a time when top strikers were at a premium. I think you'd be hard pressed to argue that he's top class. If Lukaku never improved from here on in, he'd still be a perfectly serviceable, second tier striker for us, albeit one who is prone to fairly pronounced peaks and troughs in form and who, at the very least, could be said to have a no-better-than-middling record against good sides. He scores goals in bursts and isn't really going to win you that many games through moments of individual brilliance.
All that said, give him support and good service and he'll score plenty of goals. And it's easy to forget that he's only 24. I don't think he'll ever be the most subtle or clever of players, but he can develop his game and find ways of adding facets to his game that will make him more difficult to defend against and add a few more goals to his game when he's not playing well. And, if we somehow decide to stop cnuting the ball at him from 70 yards away, well, that might help too.
Some good and true points, but also something a cynic (me) could twist and turn. First of all, we did not intent to buy a second-tier striker and we certainly cannot and will not accept so-called bursts followed by barren runs. The last point is purely psychological and must be handled, in all honesty this describes a huge weakness and should not be tolerated if you are the striker of Manchester United. We cannot play the Champions League-final and ask ourselves if the striker will be bothered that day so to speak.
We will always give him support and good service (on the pitch at least) for him to score plenty of goals, we are Manchester United after all. The same thing could be said about a lot of strikers though, and being a striker is not necessarily about scoring x amount of goals. A striker can in theory score 10 goals in five games against relegation fodder, then 10+ more over the remaining 33 games - which in total looks good but of course it isn't. A striker is judged by his contribution over a season, both in terms of goals, assists and general play. Last but not least, he must/should be the guy you would put your money on to tip a game in our favor. To go back to your point; with the level of service United offers, players like Vardy, Giroud, Llorente and Benteke would score "lots of goals" as well if they played every game. Lots of goals isn't necessarily good enough, which we have clearly seen today, against Stoke and Liverpool amongst other. When you get that only chance, you need to put it away more often than not when it matters the most. My problem with Lukaku is not only his inability to control a simple ball or find someone with a simple pass, but rather that he seems lazy and does not fight hard enough. He is just going for the first ball or working for the obvious chances, he does not stiff around and he does not give that extra 10% when the ball has gone out of the box for another player - he often just stands still with his hands in the air, instead of trying to find space for other players to play him in. Today was his chance to silence everyone, but he did the opposite by quite some margin. His first mistake was by just "being in the box" instead of actually paying attention, the second mistake was by just whacking the ball instead of actually thinking with his brain and the big miss was because of again not paying attention and being focused. Big no-no's!
We have been serving excuses for way too many years now, bigging up players because of hope rather than sheer impression of their true ability. I am certainly not giving up on Lukaku, but there are no room for sentiment in a billion dollar-industry - and Mourinho must start to look for option B and C. Letting him play forever to catch a goal is not the only solution, the guy has scored one league goal in the last nine games! He has scored against West Ham, Swansea, Stoke, Everton, Southampton, Crystal Palace and Newcastle in the Premier League - pretty much all of the bottom teams.