May very well be the same buck. The second year's pictures are definitely of a buck a year older. If someone forced me to make a decision, I would say it's the same buck.
Don't assume bucks always increase in score with age. That isn't always true. In fact, I'm amazed at how often I've seen bucks peak in score at 4 1/2, then decline at 5 1/2 (although adding mass).
But definitely no reason to "take him out." You just never know. Perhaps that buck spent precious resources fighting off an illness, and that's why his rack declined. He may jump back up nexxt year. But honestly, he loooks like a fine trophy this year!