HaLeiVi: Where;s that Gemara? I don’t think it exists. Those are reasons given in the Achronim, but the more Pashut P’shat is that it’s about Chiyuv in Mitzvos (see the Gemara in Shabbos about those 3 Brachos and the Rishonim there).
And the Rambam’s Shittah is not that Machlokes can only come when there’s Shikul HaDa’as. I mean, it is, but he thinks that Drashos are subject to debate too. As long as you follow the rules, you can Darshan out any Issur/Mitzvah D’oraisa. Thus, the Drashos can constantly change and therefore the Halachos can constantly change. Lo Shimshu Kol Tzorchan means that they didn’t learn enough to properly understand which of the 2, 3, 4 etc. Drashos is the most likely and that’s where Machlokes came from. It’s not just about new situations. Potential for different Drashos always existed. But when there was a Sanhedrin and a stronger Mesorah they were better able to outvote minority opinions and explain to the Talmidim which Drashah makes more sense and why. When we lost that, the potential Drashos still existed, but we were no longer able to properly understand and outvote minority opinions.