Yes, you are right - the Serbs were the victors of WW one and held a relative majority. Thus they dominated interwar Yugoslavia and suppressed the others, especially the Croats (the dread of the Ustasha didn’t just suddenly fall from the sky).
Even Tito, though not a Serb himself, mainly relied on Serbs for support. Especially the Tito era army was heavily Serb officered.
I think a key point about the failure of Yugoslavia and indeed the entire situation until Kosovo split was that the Serbs had hubris.
Instead of quietly assimilating the other peoples, they had to push.
I think this is understandable looking at 19th century Serbian history and its constant political strife throughout the 1800s. They even pushed the Montenegrins away.
If you contrast this with what the Parisian did in assimilating Gascony, Normandy, Brittany, Occitan, you can see that they (the Parisian) were far more successful