I think there is a problem here, but I don't think think that's the right problem. Not having these arbitrary technical limits is a good thing - for instance their service didn't degrade due to an unrelated problem. Regulating cost indirectly via some other metric is a very oblique way of solving the problem

The right solution would be throttling of spending - easy way to set proper limits, good notifications etc. It's possible to set up all these limits but nowhere near as easy as it should be. Also, how easy would it be for Google to send you an email saying "your spend looks a bit different than normal due to this traffic here"!