Well i don't really agree with you, while i agree it's inadequate for the task i've asked of it, most would be, potentially throughout the album there are tens of thousands of files.
I agree Zenphoto itself as a gallery can handle this amount of files dynamically with ease, that's why I'm using it.
What I'm getting at is I don't think it's the cleverest thing to do to have zenphoto have to create a list of every single file in a folder (and all nested folders) just to create the album, when the random thumbnail will often suffice. It's hardly efficient to demand that every single time when it's only a percentage of people who will want to assign a thumbnail. Surely an option or checkbox which initiates that would make the creation of dynamic albums quicker and reduce unnecessary calls to the server.
Now, I'm sorry if I offended you, I couldn't do it any better myself and so I just have to learn to live with the limitations and find a way around it, I was just putting it out there as it seemed like a sensible thing to bring up, and perhaps a suggestion for improvement in making the software more efficient and user friendly.