Horvath has the lead over Nabers
Unofficial and even early official depth charts tend to play the upside of rookies on the roster very conservatively. Just looking at this chart, Isaiah Spiller is buried at "RB5". In Tennessee for example, Malik Willis is currently listed at QB3. The nature of rookies having to "earn it" has always made it difficult to evaluate where their actual placement on the roster is.
That's why Zander Horvath having the FB1 designation over Gabe Nabers at this time is surprising. Based on historical trends, you'd expect Horvath to be FB2 and eventually earn that spot over the incumbent. But the fact that he's already listed higher is surprising.
Like the right tackle battle, this comes with the huge caveat of the -OR- as all the offensive competitions do. That being said, it's always felt like this was Horvath's job to lose coming into camp as opposed to a real competition. The Chargers used draft capital, albeit a 7th, on a player whose upside is offensive versatility.
The preseason will give us more insight into the competition between the two players, but the first depth chart is a rather loud endorsement for Horvath compared to other rookies in his draft class.