Oh, the OS treeview is dreadful, everyone who's seriously coded on Windows knows that.
As to actual complexity curve (which, knowing what I do about NTFS, I'm fairly sure is O(n log n)), I don't really care about it; since it hasn't shown up in a serious way at n=100000, it's unlikely to realistically affect anyone badly. Even if 1 million files (in a single directory!) took 18.5 seconds, it wouldn't be pathological. Other limits like disk bandwidth and FS cache size seem like they'd hit in sooner.
As to actual complexity curve (which, knowing what I do about NTFS, I'm fairly sure is O(n log n)), I don't really care about it; since it hasn't shown up in a serious way at n=100000, it's unlikely to realistically affect anyone badly. Even if 1 million files (in a single directory!) took 18.5 seconds, it wouldn't be pathological. Other limits like disk bandwidth and FS cache size seem like they'd hit in sooner.