Potter's character was certainly better than Blake's, IMHO. The bumbling, philanderer was essentially the Blake character and it's hard to take that role and that character to new areas. Plus, the writers were still finding their way the first few seasons, and Alda's influence was less back then. MASH was one of those few shows that not only lasted and survived year after year and cast change after cast change, but did so only by getting better, year, after year. The introduction of Potter and the establishment of him as a pivotal character, to me, showed one great example of just how great that show was.
Make no mistake though, changing cast like that and bringing in new characters is not really viable without really good actors. David Odgen Stiers, Mike Farrell and Harry Morgan (sorry if I misspelled any of those names) are/were all very good character actors...some of the best. They made you believe you were watching real people and real life. That's a rare talent and gift, and when there is so much bad acting these days that actually tends towards cringe and throw-away TV, when we lose an actor like Morgan it is truly a sad day.
RIP Harry!
TJR