This is a fair assessment, in that all the gaudy stats and numbers are meaningless if the Chargers just don't use him.
Looking at some numbers, the big stat that would be cause for concern would be the role of the TE overall in the Chargers' passing offense. Looking at target share over the years:
2013: 27%
2014: 24%
2015: 24%
2016: 26%
2017: 21%
There does seem to be a fairly discernible drop-off this year. I guess the question is whether that is an aberration or a trend.
This is the game-by-game targets for all TE in 2017: 3-12-5-8-11-8-6-4-4-9-7-13-9-6
I'm not sure I can see much of a trend there. A lot of variability, and certainly Hunter felt that with two zero-target games.
I guess for me I'm just hard-pressed to see why the Chargers wouldn't use him as a featured player going forward. As you noted, he's done nothing but produce when given the chance.