The establishment of alliances will have the most dominant effect on the factions nearest to you and the ones that are bordering them. However, by establishing alliances with distant factions you can still have some control over events on the far end of the map. I generally do both. Is it really going to matter to you who is the strongest faction you have to fight when you expand toward Rome and have to fight Carthage, or the Scipii, or the Brutii, or the Greek Cities? Or some combination thereof?
Yes. Because if the Scipii overrun Sicily early on, they might have more than hastati and velites. If it doesn't matter, then have no AI vs. AI battles and the player can just conquer a static, unchanging world.

And, if alliances are so key, I still can't understand how Scipi overrun Sicily without save/loads and do nothing with save/loads when THEIR FACTION IS LOCKED INTO ALLIANCES WITH ALL THEIR LAND NEIGHBORS EXCEPT IN SICILY.

Not to mention the script or Senate missions that always lead Julli and Brutti to take Segesta (?) and Appolonia like clockwork. I assume Scipii get the same marching orders to take Siciliy, but when it's save/load it somehow goes away?

Scipii are already allies with the other Romans. Without loading they seize all of Sicily. With loading, they do nothing. And somehow the butterfly wings of the player's alliances would alter this result?

Maybe for Greeks and Carthage who definitely can be busy elsewhere your points could be valid, but Scipii? And keep in mind if you are a Roman faction, it will affect your end-game civil war if the Scipii have not expanded enough.

Now, in games where I did not save often, I saw Scipii do better than Brutii...could it be a way to slow down certain factions?