He consistently hits, and while he isn't a star power hitter, he does everything else so well. He's been 43% better than Triple-A average this year. 88% better than Double-A last year and 43% better than league average on the whole last year.
To put it another way, last year Nathaniel Lowe hit 16 home runs and was a 121 wRC+ hitter at the 1b position last year. His ISO was .136 - this is lower than Long's ISO in Triple-A right now. He can be that guy. Pete Alonso hit 34 home runs but was a 122+ wRC+ hitter. Power at the position is cool, but Long was just as good despite.
Jonathon Long might not be a 30+ home run guy. But his batted ball data is really good. I think we have to accept he's going to be a different version of a 1b/DH, like a Lowe, but it doesn't mean he can't be good.