While Harry Morgan was a good actor, it sometimes seemed like they really didn't know what to do with the Potter character a whole lot. All the Mash characters were pretty one dimensional but it seemed to grow stale with his more than the others.
The big exception for me was the tontine episode with the bottle of wine he and a group of his friends from WWI had saved for the last survivor to drink. I thought that was a well done episode.
Of course, Henry Blake was kind of the standard sitcom goofy neighbor/goofy boss character. But it worked well for the short time he was on the show.
I do agree that Winchester was a much more well rounded character than Burns. Winchester could hold his own with Hawkeye and BJ. Burns was over the top which worked as a foil in the particular time that the series was started but I think it may have been just as well that the actor left when he did.