Depth should be widely acknowledged to be much better with the exception of the QB position.
I don't know if the OL are built to be better run blockers than 2017, though I also can't say they're built to be worse run blockers, but they are most certainly built to be better pass protectors in 2018 than they were in 2017. And they weren't bad in pass protection in 2017, either.
Josh Sitton is an obvious upgrade particularly in this pass protection department. It's straight forward in that he's a guy who is better at certain things than the people that played here before him.
There's a tough comp between Mike Pouncey and Daniel Kilgore only because there's no way Pouncey should have played 16 games last year. We got really, *really* lucky in that regard. It just shouldn't have happened and I think the Chargers are kidding themselves. If you stack up what Miami got out of Pouncey one year ago versus what they can expect out of Kilgore this year, then as you suggest we might be talking about more or less a tie, although there is one important factor that is clearly in Kilgore's favor which I'll get to in a second. However if you're stacking up 2018 Mike Pouncey (now of the Chargers) with 2018 Daniel Kilgore (now of the Dolphins), I think you have to take Kilgore hands down because he's about the same quality on the field, and you should expect him to actually be on the field for the season whereas it feels like the Chargers will be lucky to get 8 games out of Pouncey.
On the other hand, there is one important factor working in Kilgore 2018's favor versus Pouncey 2017, even accounting for Pouncey having played all 16 games. That is the amount of practice work Pouncey missed because of the plan they developed for him to try and get him to play all 16 games. The plan WORKED, and is a testament to the skill of our sports performance, training and conditioning, and analytics staff. They should be applauded. But the plan had big drawbacks. He never practiced, and as a result the chemistry of the line suffered, particularly toward the beginning of the year. Daniel Kilgore is a cerebral guy, noted for how quickly he can digest a new playbook, and he will be practicing all spring, summer, and autumn with the same four guys around him (Tunsil, Sitton, Davis, James).
That should improve the OL's effectiveness in ways that may not be quite as obvious as seeing a guy on the field that has better anchor or better mobility, etc.
The other upgrades on the OL are what we in my business might think of as either evolutionary catalysts, or based on easy comps.
Ja'Wuan James only played 8 games. Could that happen again? Sure. Is the expected value of his 2018 games played at 8.0? No. He's played about 72% of his games in the pros, so you figure 11 or 12 games in 2018. But I would argue that number is low if you account for his college career, where he was an injury-free stalwart. He doesn't have degenerative issues. I would argue that he might be more in line for some upward reversion to the mean in terms of his health and availability. I am personally thinking 13 to 16 games but that's just me. And he was one of the best right tackles in football when he did play, so getting 4 to 8 more games out of him would be a pretty nice sized upgrade.
Jesse Davis played his final 6 games at right guard. He played right guard better than he did left guard, particularly in pass protection. He's already been declared the starter at right guard. If he simply plays the full year at right guard the way he did the last 6 games then Miami will have a second upgrade on the guards unit. On the other hand, if the better play for those 6 games was more or less some random noise, small sample stuff, there could be a reversion, and perhaps we do not see an upgrade versus 2017. But there's an evolutionary catalyst lying in the wait here. Last year was literally his first year playing NFL football. He'd been around the NFL a year before but hadn't played. Don't young players grow with experience? Isn't that a thing? Especially as they stop being moved around and are allowed to focus on one spot? It's not something you should BANK on, but it is something that you should expect to be true more often than not.
Same with Laremy Tunsil. He wasn't actually that bad in 2017, penalties aside. But he was in his first year playing NFL left tackle. Don't we expect, as a matter of default, young players to grow as they get more experience? Especially true if they're former high picks with great tools.
So overall I think the outlook of the OL should be very good. Expectations should be high in pass protection, though a little less clear in run blocking.