It makes sense to say “the hottest year on record” if “practically every year is the hottest on record now” and you’re talking about the most recent year.
Does it make more or less sense than “Another year of record breaking heat”?
“Hottest year on record” is like a child stopping on each step of a staircase saying, “I’ve never been this high!” It’s correct, but doesn’t mean much in context, and gets old real quick.
“If I take one more step, this’ll be the farthest from home I’ve ever been.”
Though unlike the hypothetical child or Samwise Gamgee, what we’re doing is going to create suffering for very large numbers of people. It’s probably also a reliable source of clicks for online media organizations.