The problem is they hide this problem away and in no way warn you, I fully accept that they might not want to prioritise fixing this, I just ask for common courtesy - I had a month with dropbox basically not working at all. Popping up a warning isn't bending over backwards.
I wonder what would happen if this occurred on gmail - you have too many emails so suddenly it stops working without warning, completely, irrecoverably. Would you still make the 99.92% vs. 0.08% argument? Or would you find it a bit off? At least warn + give a way out...
My friend, I don't believe you realize just how outside of the norm you are. 300k files is quite a large number of files for even a local file store to choke on.
But there are actually two things that put you outside the norm. First, it is likely only technical users who are going to acquire 300,000 files in their DropBox. Second, technical users are already typically aware of the downsides of storing tens of thousands of small files on a file system and how common it is for even dedicated local servers to choke on them. We all have copied 300,000 small files and have it take f-o-r-e-v-e-r and then copy one file of the same aggregate size of the 300,000 small files and it flies through the copy. Why would DropBox be any different?
I wonder what would happen if this occurred on gmail - you have too many emails so suddenly it stops working without warning
Here's an experiment for you to try. Write a program that sends you 60k byte emails as fast as it can. When you get up to 300,000 emails see how well your Gmail account works.