This could be argued until the end of time....bottom line is, if your worried about transom weakness then buy a transom saver, if you think your motor mount is solid, then take the gamble. No one can make you decide, your boat....
FEAR sells
I have just tipped both motors all the wayup and latched them. That position removes ALL the outboard weight from WAY behind the transom. It now sits right over the top of the transom Preventing any constant pulling outward of the transom. Even on severe road bumps. I do strap the transom to the trailer.