Nope, should be very strong
I'd use some sort of oil like Penofin
You fill the hold with concrete and use a mounting braked for the post. Structurally, the concrete and post will perform well and the bracket serves two purposes. It keeps it lined up and more important, keep it from ground contact and wicking up water to rot it away. Your 10 x 10's may have character, but are more prone to rot than a pressure treated post.
If you are in the process of starting a deck, you can get a lot of information on brackets and fasteners at