My opinion is that Jedi mistook to wait, but also the Republic. The Senate waited a decade to intervene, allowing to Mandalore to create an Armada. If the Mandalorians had always been a threat for the Republic, why permit them to grow and to get stronger? A dreadful war and his worst consequences (Malachor battle and Revan's fall) could be avoided by preventive actions years before (it's my opinion).
Why Jedi and the Senate were so blind? Was fortuitous, or behind the scene there was the Emperor's hand?
p.s.: sorry for my bad english
The Republic had no authority on the majority of the Outer Rim colonies. They were not official members of the Republic. The Republic had to let the colonies defend themselves. But if they were members of the Republic, the military would have intervened and destroyed the fractured Mandalorian armies. This was a brilliant tactic by Mandalore. Attack planets that the Republic can't defend, while gathering more clansmen, acquiring more weapons and supplies, and conscripting more soldiers. He took advantage of Republic law to build an almost unstoppable armada.