This is where folks like you (and Chiefs fans) tend to miss the big picture. This isn't merely about blocking; yes, Gronk (and Kittle) are outstanding blockers. But if it were only about that, the team could just put in a backup tackle, call him a tight end, and use him for extra protection. Being a dual-threat like that changes the entire offense; teams cannot put in the right personnel considering a guy can either be an extra lineman or can streak up the seam for a huge game breaking play.
Absolutely, having a TE in last year's Super Bowl like Gronkowski would have made a pretty big difference. It changes everything about the running game, playaction, and the ability to punish the defense for being underaggressive or overaggressive.
Kelce is awesome...a huge advantage overall...but frankly there are few, if any, offensive players who can even compare in value to prime Gronkowski or Kittle when he's healthy and at his peak.