I generally don't recommend tire carriers if you can carry a spare in the bed. Multiple reasons have brought me to this conclusion.
1- they are never as strong as they need to be to keep the carrier from bouncing, rattling or swaying. I have even seen them break from lack of triangulation and too much leverage.
2- departure angle can be compromised depending on the design.
3- rear view can be unnecessarily obstructed.
4- backing up into things is a problem, because you can't see.
5- weight, as you mentioned, can be a problem as well. Mounting the tire closer to the cab of the truck distributes the weight more evenly.
The strongest method of latching a tire carrier, to keep it from rattling and to better control the swaying, is by a wing bolt which I usually make out of a 5/8 bolt with a handle welded to the head. But they are a pain to use. The latches you commonly see on tire carriers don't hold well and stretch over time.
These are opinions based on my experience. Others love them.