Rhoda was considered very unlikeable early on, leading to uncertainty about the character. It was suggested to make Bess fond of Rhoda so that the audience would see the character through the little girl's eyes.
Apparently, the studio audience hated the first shooting of the pilot (there was a bomb threat, the AC was out, and the audience were afraid for poor Mary because of Rhoda's caustic first scene). No one laughed and Mary rode him in tears, her husband, Grant Tinker -- who had put the entire production together -- called Brooks & Burns and said, "fix it!" (Tinker joked later that "fix it" meant absolutely nothing and was no help at all).
Script supervisor Marjorie Mullen, who'd also worked on THE DICK VAN DYKE SHOW, recommended little Bess advocate for Rhoda, Bess telling Mary that Rhoda was really a terrific person. Thus allowing the audience to view Rhoda in a different context than simply "mean".
Otherwise, there were supposedly no changes. And the second night they re-shot the pilot, the audience roared with laughter. The test audiences later still hated it, calling Mary "a loser" because she was single at 30, and uncomfortable that there were "two jews" in the cast. The network had similar concerns, assuming their great star, Mary Tyler Moore, was going to be brought down by a disastrous production company, with "awful" scripts that were character-based and structurally unrecognizable from '60s sitcom scripts which were line/punchline/line/punchline, etc...
But CBS had a 13-episode commitment for the show, so they decided to bury it in a dead-end timeslot on Tuesday night, initially scheduled against MOD SQUAD (which was #1 in the ratings that summer).
Ethel Winant, the casting director for CBS, however, loved the show and its early scripts, and agreed to cast it. She found Asner, Leachman and a completely unknown Valerie Harper whom Winant had seen in an off-Broadway play (whom she had to scramble to find, as Harper belonged to no guild whatsoever). As Allan Burns said, Winant defended the series "almost to her detriment" to the button-down all-male brass at the network who universally hated it.
Then, network consultant wunderkind, Fred Silverman, was so impressed when he screened the finished pilot -- edited and scored, with the opening titles -- that he called New York in the middle of the night and told the CBS brass that they needed to move MTM to Saturday nights (just before MISSION: IMPOSSIBLE), or this great new show was going to be lost (which had been CBS's intention). In an era when fall schedules were set and adhered to months in advance, the advertizers apoplectic over any last minute (or even last month) changes.
Jay Sandrich, who had directed the short lived HE & SHE (a partial inspiration for MTM) was brought in to direct. Sandrich looked at other contemporaneous 3-camera sitcoms and disliked how the actors seemed to be yelling at each other, because they were playing to the audience. Although MTM also used the 3-camera method, Sandrich directed the actors to pretend they were making a movie. Thus, MTM avoided having the deafening tone of other sitcoms of the
Although it seemed to take them about a year to rein it in, as the first season indeed has that "too loud" '60s sitcom delivery. Not that I mind very much, but I'm glad they subdued it pretty quickly.
BTW: Joan Darling, who five year later directed "Chuckles the Clown," was almost cast as Rhoda before they were able to locate Harper.
Ms. Winant who, along with Fred Silverman, saved the show: