Back when westerns were the primary vehicle for armed violence on screen the lone-wolf attitude made a lot of sense. Westerns were about America selling itself on it's own mythology, showing us to be a nation of self sufficient free spirits, but there was also a practical reason for those men to take the law in their own hands - there weren't necessarily other authorities around who could intervene in a timely manner. But now that we've moved on from that sparse setting to blockbusters that take place around the world and the stakes have gone from a threat to one family to the potential destruction of the world, the rebellious hero who plays by his own rules makes less sense. Seal Team Six pulled off it's mission because they were well co-ordinated, and if it's one thing that the cocky alpha males in movies like Top Gun and Pacific Rim are iffy on, it's working well with others.
MacGruber is a parody of action movies - particularly of 80's action movies - and if there's one joke in MacGruber that consistently works it's the films spoofing of the do-it-my-own-way hero. MacGruber never wants to listen to the rigid military men who want to constrain him by giving him orders - he wants to do the mission with his own ragtag group of retired specialists instead of the crack staff of currently enlisted men that he's offered, and he doesn't want to use guns, he wants to use "ingenious" devices of his own making. But MacGruber's first impulse is always wrong and the higher ups who are trying to put him in check are always offering sensible advice. (Their guns fire just fine but his devices are... less effective.) If you've spent any amount of time watching action films the jokes about the hero's grand scheme - which are often no more complex than "stroll into a party the villain is holding at his own house and sneak around like an idiot" - will really connect because those types of plans are absolutely ridiculous and they are a staple of the genre.
The movie's biggest flaw, however, is in it's straight man. Ryan Phillippe plays the talented lieutenant who is assigned to help MacGruber stop his arch nemesis Dieter Von Cunth from blowing up a nuclear warhead, and he's too tight-assed in the role. Every plot point is absurd (remember: the villain's name is Dieter Von Cunth) and everything MacGruber says is insane so Phillippe's dour manner doesn't come across as a grounding force - there's no grounding a movie like this, not really - but instead it comes across as a killjoy. It might have worked better if he had the sort of chemistry with his co-star that the leads in Hot Fuzz had, but Forte and Phillippe don't play off each other very well. He's too straight in a movie that's too crooked; he feels out of place.
The difficulty that this movie has with it's straight man goes a long way towards showing why a lot of American action movies make their main character a rogue - there are a lot more ways to make the guy who makes his own rules entertaining. But I do think that it is important to call bullshit on that type of character from time to time, because the sort of myths that we tell ourselves have a way of becoming self fulfilling prophecies. (After all, Top Gun inspired a lot of people to try to become pilots.) Even if MacGruber has a lot of flaws - and miscasting one of your leads is a big one - I have to love it for it's pointed skewering of a stock character I have less and less use for as I get older. If the uptight lieutenant can learn to love MacGruber despite his faults when his life is on the line, I can learn to love MacGruber despite it's faults when I'm watching along at home.