Would broader naval treaties have worked better?

Was it an interwar blunder to leave many naval powers outside the treaty system?

Partly, but a fully inclusive treaty might have collapsed under the competing tonnage demands of several regional arms races.

A broader naval treaty would have to reconcile several linked rivalries. Russian claims would affect Japan, German claims would affect France, and South American participation would revive the Brazil-Chile-Argentina balance. The French and Italians would resist limits that left them exposed, while Russia would need to divide its strength among the Baltic, Black Sea, and Far East. Wider participation brings legitimacy and more states under the rules. Every added security relationship also creates demands that can prevent a treaty from being enacted at all.