Speculating on too many "what ifs" is indeed fruitless, but some special moments in history can be described as "turning points" which had great influence on the events afterward. I think what I'm going to say now will be highly controversial, but in my opinion, 2-nd Punic War was such a turning point for the history of the Mediterranean.

2nd Punic war could actually go either way, and Carthage had a good chance of winning it, had Hannibal received enough support from home and he himself could be more decisive in landing another blow to Romans after the battle of Cannae. But Rome was fully committed to the war, while Carthage was not. After the war was over, Carthage was in no position to threaten Roman hegemony again. 3rd Punic war and its outcome were inevitable. After 3rd war Rome was an undisputed Mediterranean superpower.

The Roman achievements that followed were natural. Rome was filling a huge power vacuum in the Eastern Mediterranean and waging colonial wars against divided Celts. I'm not trying to diminish Roman achievements which are indeed incredible, but I think their achievements were not of military nature, but of administrative. After all they've created a superpower that successfully (more or less) governed a huge ethnically diverse area for nearly 400 years, although from military point of view, after Carthage they didn't face an equal enemy that could threaten their very existence until the barbarian invasions of the late 3-rd century and onwards.