It starts and ends with Steph. A KD led team was never stopping BronI think it's more of a "then Steph AND KD happened". People forget it took the Warriors 6 games to beat a decimated Cavs team, and they lost the following year in 2016 when Kyrie and Kevin Love were healthy. Without KD, the Steph run doesn't happen
The better hypothetical would be if KD stayed in OKC and you had 3 MVP caliber players on one roster (KD, Russ, Harden), have a Dynasty, and that would halt Lebron's title runs
Not to mention the 2022 finals which steph won that got him tied with LeBron in ring count