I think it's fair to say Gronk has faced two issues that have prevented him from being as effective this year as he was last year. First, he's still dealing with lingering injuries. Second, he was double-teamed heavily in the first three games.
It's worth noting that Kelce was also dealing with lingering injuries (a sprained ankle) in the first two games of the season. Kelce played almost every snap in the first two games but only ran 11 and 13 routes in those games. In the first game he did nothing, catching 1 pass on 6 targets for 6 yards; in the second he caught 7 passes on 10 targets for 109 yards and 2 TDs.
Gronk has run between 22 and 34 routes in each of his games this year, with the 22 being the Dolphins game where he missed a large chunk of the second half. The Patriots have actually averaged marginally more pass plays per game than the Chiefs have, and Gronk has run a route on more of those than Kelce (though Kelce's are dragged down by the first two games). Last year, both players ran a route on 90% of their team's pass plays. This year, it's 77% for Gronk and 68% for Kelce.
All this is to say is that, while Kelce has clearly recovered from his injury, Gronk is still probably feeling the effects and was limited in the early going by the ineffectiveness of the Patriots' offense. Gronk is likely to see a resurgence while Kelce will probably not maintain this torrid pace, especially given that he plays for Andy Reid and the Chiefs, a group notorious for fading fast. We'll see. Can't take anything away from Kelce. He's still not as good as Gronk though.
