Good point; even an unsuccessful assassination attempt by Princip - let’s say he only lightly wounded the Archduke - would still have the Austro-Hungarian Empire breathing down the neck of the Serbs, who in turn would’ve appealed to Russia for help; Austro-Hungary mobilizes, then Russia, then Germany, and we have still the exact same scenario.
At that unfortunate point in history, probably ANYTHING would have served as pretext for war. Hell, say the Archduke eats some bad goulash and gets Montezuma’s Revenge or food poisoning; the Austro-Hungarians then maintain it was attempted assassination by arsenic or something and the same scenario unfolds.
Righto. The Austrian/Hungarians saw Serbia, probably accurately, as a mortal threat to the peace of their empire.
So they wanted to destroy Serbia in a short, victorious war. This of course dragged in everybody else, and pretty shortly the Austrian/Serbian issues was forgotten by everybody except those directly involved.
But even with the massive predominance of the Austrian forces relative to those of Serbia, Austria was repeatedly defeated till big brother Germany rode to her rescue in late 1915, assisted by a surprise attack by Bulgaria.