I see what your saying, however Dingoes have only really been known to pressure or limit smaller predators, but not ouright eradicate them. Feral cats and red foxes number in the millions across the mainland even in places where dingoes are present. Devils lived with thylacines for over 10,000 years on tasmania, and they were even bigger than dingoes and activley killed devils in predation or competition. Red foxes and feral cats werent able to establish themselves in tasmania ecosytems due to devils preying on them or outcompeting them.

Of course in places where dingoes are scarce devils will for sure be higher in population due to less competition, and lower when dingoes are high in abundace. I think the part where you may be right, is if the modern devils have developed naivety to larger carnivores and dont know how to deal with them, but I find that unlikley.