We're not talking about an invasion, we're talking the plundering of your natural resources and more signficantly piracy. Once these guys discover you're helpless, then the trouble starts. Try life on the North West coast of Borneo and in the Sulu Sea if you want a taster.
Malaysia and Indonesia don't have enough air assets to control their own airspace in the region. The pirates are willing and able to fight it out with the Malaysian and Indonesian coastal forces. Fast Jet bombers would make a considerable difference, believe me.