My wife used to work as an engineer approving (or demanding changes) to plans for Toronto. The biggest problem is that developers will cut every-single-corner and later plead ignorance when they build the 'wrong' (cheaper) way.
Here's what would happen in the scenario you're describing: Developers would build whatever the heck they like. Then, they'd be told "You built something that doesn't meet code". The developer would say "Well, my mistake, but it's built now and do you really want to tear down this new housing development that people paid for 3 years ago?". Now you have a political situation where the people who want to move in are being told that the building has to be torn down. Politicians would get involved, and the building (not meeting code) would be allowed to stay.
This would repeat over and over again.
I completely agree that we need a straightforward set of clear, consistent rules. But the idea of pre-approval without checking what the developer plans to build, how they plan to deal with waste-water, storm-water, parking, and a long list of other requirements, that's asking for trouble.