I agree with you all, yes Motown made them stars, but they didlimit them a lot and many of the songs they recorded were merely fillers and songs that had been done to death by other artists (Forever came today -although their version is great, with Marlon doing the vocals!!). Also as they really lost their prominence in the later 70s. By 1978 all they really had was Stevie Wonder, who was smoking, The Commodores were breaking through, Rick James and everyone else was in erratic form (Marvin Gaye etc).
Michael and his brothers with the support and urging of Joseph, knew they needed to move to a different label, where they could write their own songs and record more upbeat music, as Motown was stuck in this 1967 showtune type mold with Norman Whitfield gone and many aging acts like the Miracles, Smokey Robinson, the Temptations and Four Tops on the books (In the period where their best days were behind them, but before the big 80s revivals). Basically they got off a sinking ship.
That's not to say the music they did on Dancing Machine and Moving Violation wasn't good it was, They still had hits with Dancing machine, I am Love Part 1 and 2 and Forever came today, but they felt they were stuck in in that mold, and they were no longer a bunch of little kids, by 1975 even Michael had hit puberty and Randy was no young Michael. Jermaine was the thorny issue being Hazel's husband. Plus that split was acrimonious, Berry Gordy took and kept the Jackson 5 name and that pissed Joseph and the guys off no end as that was their name they used back in Gary. Hence why at Epic, they became the Jacksons.
Plus too to make it bitchier, Motown kept issuing compilation albums of old Jackson 5 music under the Jackson 5 name, usually at times when Jackson product and solo Jackson music came out on Epic and other labels. Sometimes this music was a hit with songs like "One day in Your life" and "Farewell my summer love" great songs, but MJ was not profiting of it. The quality varied ranging from demos in the 1968/69 period to better items. All of this backstabbing would grate on Michael after a while as in the 80s and most of the 90s, he was very shrewd and knew how to manage al his money and affairs and obviously did not like Motown undercutting him, when a song by 13 year old Michael competed with the current album.
But I don't think Michael would ever had gone back afterwards, I mean Berry Gordy had to beg Michael to do the Motown 25 show and even then it was on the condition he perform Billie Jean on it as well, and thank God he did!!!