They would not learn how to build an empire. Their little confederation in Italy was meant to fend of Greeks and Gauls. Maceondon or Egypt might end up being the prominent power in the Mediterranean (although not as dominant as OTL Rome)
Empire is the most fluid type of society, any government can do it - republican city states, monarchial dynastic states, theocracies, you name it. I doubt it would be much harder for the Romans in this timeline to figure out how to make it work for them.
A traditional marking point at which Rome became an empire is the creation of the first province, Sicily. I don’t see any reason why Rome couldn’t expand into Sicily in a Sans-Carthage TL, unless Sicily is tied to a larger Hellenistic state, but even that is not likely to be a long term matter. Anyway, once they do it once, they can copy the model elswhere, just like they historically did.
On the other hand, given a Sans-Carthage Sicily, its possible Sicilian society might be more amenable to being incorpoated as Socii. On the third hand, they might be taking the place of Carthage as the mercantile power in the region, which could make them less amenable to being incorporated as Socii.