If Bay hadn't had the balls to take on the project, the trilogy might've ended up in the hands of someone truly dreadful like M. Night Shyamalan who I still haven't forgiven for what he did to "The Last Airbender". It could've ended up like Dragon Ball Evolution or Tekken, but it didn't. Just because we can think of stacks of better directors, it doesn't mean that any of them would've wanted to put 5 years into a trilogy about transforming robot kids toys or have even been capable of bringing them to life in such a believable fashion.