People SAY that, and on paper that seems like a decent solution, but despite the overlap, the tones are really different, some details are shuffled around, and there's no truly clean splitting point. Like, the death of Hughes is when 2003 starts really going in its own direction, but its really changed everything with Scar prior to that, added and lost things with Barry the Chopper, the timeline for Yoki is different, the brothers are there for Hughe's wife giving birth to Elicia while in Brotherhood they're present for a different woman giving birth years later, while Brotherhood at that point has introduced a couple of long running characters, and so on.
Maybe, maaaaybe if you just go through the very early flashback stuff and stop after say, Nina's death, it could work but that's only like episode 8, what would even be the point? Plus what happens to Tucker afterwards varies a lot between the two series, in one version he's killed by Scar and in the other they're just lied to and told he's dead so he can pop up against 40 episodes later.
There's just too many little things to do a clean cut on.