I was one of those pointing at Dillon as being more of a fullback/H-back, because his blocking skills far exceeded everyone on the team at that time. That would still apply.
What Dillon adds to that role is that he can be a power runner for short yardage as well, and has decent enough hands that he's also a threat in that department. Role players, in today's NFL, are a necessity, because the have a combination of skills that make them a little different kind of threat, and support, for others.
As an example, a good blocking H-back/fullback can be important in picking up pass rush from the blind side of a QB, saving them from being pressured, or taking a hard hit that can disrupt a play. Bill Walsh turned that role into one of the backbones of the 49ers offense, and it worked to perfection. LeFleur has that same offensive approach to the game.
As for Jacobs, he's done everything that they've asked of him, including carrying the team in a game where they went in concerned about having to throw the ball. His efforts in that game was enormous, and every down that he's in the game, the opposition needs to honor the run because of his chops between the tackles, even on 3rd and 9, because he's good at finding seams in defenses.
What we're seeing with him in the lineup is more balance to the offense. He's more consistent in his runs than Jones was. A steady 3 to 5 yards a carry far exceeds the 20 yard carry then four more where you don't get a yard. You move the markers, then the chains steadily down the field, and wear the opposing defense down, and keeping your own defense fresh.