Colonel Blake was an inept idiot when it came to military protocol, sure. But he was a conscripted doctor. He did not want to be there. He did not like confrontation and was lax when it came to enforcing military stuff. When it came to managing the doctors and nurses to get the job done medically, however, he was very competent and well respected. Their MASH unit had one of the highest survival rates, which they were lauded for. Everyone loved Blake because he was a decent guy trying to make the best of a really bad situation (he had no prior experience in) for everyone. He did leave early on, and it was one of the saddest episodes of the show for the characters because he was shot down over the sea of Japan.
The only one who was portrayed as truly incompetent at his job was Frank Burns. BJ and Hawkeye were constantly giving him shit for bungling his operations and not giving his best to the patients. He left before the halfway mark. This was a continuing plot point.
When Colonel Potter came on board to take over as XO, he was an ex-military man and much stricter in enforcing proper military protocol. He was often frustrated by Hawkeye's insubordinate actions and attitude (which was Pierce's way of giving the war his proverbial middle finger), but he couldn't deny he was his best surgeon who always came through when lives mattered.
Winchester was a snob, who thought he was superior in every way. Then he got posted to MASH and had a very rude awakening. That said, he was still an excellent doctor who performed well in the operating theater.
MASH did a fantastic job giving different perspectives on the war, how some people wanted to be normal civilians but were conscripted against their will - like Hawkeye, BJ, Klinger, etc. While there were others who were pro-military and wanted to do their part - Colonel Potter, Major Houlihan and Frank Burns.
What made the comedy so sharp, while not detracting from the moments of drama, was how it came from the clash of personalities thrown together into a tense, high stakes situation. People were stressed to the max, trying to deal with long harrowing shifts, dying patients, dysentery, the threat of shelling and disgusting army rations. Hawkeye often was on the brink of a nervous breakdown. He was our mouth-piece for how absurd, arbitrary and dehumanizing war can be. So the humor works because it's very character driven and situational. It's a way for these characters to cope. MASH was a comedy which actually delved pretty deeply into the personal toll war takes on an individual, a community and to a lesser degree, a nation torn apart by civil war.
