How did it work in past games? Do you have a sample of the old mechanics?
I don't remember how it was done in Basic D&D, but it was probably less complex.
In days of yore, there was a way to capture dragons by subduing them. Should the new edition follow suit?
If you mean that the PCs should be able to choose whether they want to subdue or capture a dragon (or any other monster) rather than killing them, of course yes... how can you disallow that? They can do what they want!