My app is occasionally (once per day) running a bulk insert of around 1,000 files. After a handful of inserts I start getting 403 rate limit responses. Since my app does the inserts sequentially, my attempted insert rate is never higher than 1 per second.
I've checked that I have billing enabled and that my quota limits are 100+ per second, so I don't understand why I'm getting throttled so aggressively. The consequence is that the insert is taking over an hour which isn't a great advert for Drive :-(