Drive has plans up to 30TB, so it would be disappointing if 10-20TB counted as unusual w.r.t 'unlimited' plan.
Google Drive with 30 TB storage is priced at $300 per month. But then you have Google Drive for Work with unlimited storage and is priced at $10 per user per month. Meaning that you can get 30 users with unlimited storage for the same price. Why in hell would anyone pay that?
In an enterprise environment that I'm familiar with that has 100k users on a shared file store solution... Something like 10% of users use less that 1GB, the 99th percentile user uses 1TB, the 90th percentile users is something like 30GB.