Having an exception process is ripe for abuse. We have laws for a reason: it is generally a good thing for the same rules to apply to everyone. When you require an exception, you can easily threaten and extort whatever you want, because the "default" is to deny an exception to a rule. We see this all the time with planning: planning commissions extract expensive "concessions" from developers all the time. "Oh, you technically can build that much, but it won't be profitable with all that parking we mandate. We'll gladly grant an exception, if only you capped heights, and have fewer studios."