Whoa, that does seem like a high loss rate. I'd say that I might lose a couple per year... though I don't have a ton in my 300. There are 3 very big turbos (baseballs) and maybe another dozen smaller ones. Some trochus as well but I doubt it's more than 10. And there are a few money cowries wandering around and I'll see them infrequently. Seems to be pretty well balanced. My guess is there are just too many and not enough food in your system (and other's from the sounds of it).
I guess that’s possible. But I’m still decently below the suggested numbers for my size tank. And there seems to be enough growth on the rocks. I wouldn’t think any of them would go hungry. But maybe there really isn’t enough of what they need?
Here’s a photo from today to give an idea what my rocks look like currently…

