i think this can you only test with the new jD version 2.5.x. In this exist now a new layout only for the singel category view. But i am not sure that your wish is really possible. I have not try it.
In layout needs to remove <h1> tag.
In file jdownloads.html.php needs to add <h2>
and needs to add <h1> tag here
My mind, that your templates method is very hard to understand.
It's very hard to make some changes, because it needs to edit core files.
For example, k2 template system are brilliant. Very easy to find code and change it.
After updating component all changes works perfect.
P.S. Why do I need to title were such?
Because <h1> titles is one of major things for SEO.