That seems like decent production for a guy that "can't get on the field". It's 7th on the team and 2nd amongst LB's.
Here is the breakdown.
In game one, Minter played 24 of 61 snaps (39.3%). No big deal, it was his first real game back, and the team wanted to ease him in. Bucannon, who most would say is taking his snaps, played 37 of 61 snaps (60.7%). Rivers attempts 36 passes, and the Chargers run the ball 24 times. Essentially, the Chargers ran the ball 40% of the time.
Game two. Minter has an increased role playing 34 of 72 snaps (47.2%). It makes sense, the team thinks he is healthy, and wants to see him in an expanded role. Bucannon's snaps decrease as he only plays 37 of 72 snaps. Manning attempts 39 passes, and the Giants run the ball 27 times. Giants ran the ball 40.9% of the time.
Game three. Minter's role reduces dramatically, playing only 19 of 64 snaps (29.7%) vs. a physical in division team missing it's two best TEs. Bucannon plays 43 of 64 snaps (67.2%) which is his season high. Kap attempts 37 passes, and the 49ers run the ball 24 times. 49ers ran the 39.1% of the time.
Teams are running the ball vs the Cards at an average of 40% (40, 40.9, 39.1) of the time, so actual rushing attempts aren't a factor.
With Davis and McDonald out, the athletic TE did not factor into the gameplan, and snap usage of Minter.
Essentially, MInter was eased in in game one, given more snaps in game two, and then had his lowest amount of snaps for the year in game 3 without any real difference in the % of time the opposing team ran the ball. Also in these games, Bucannon's snaps started higher, then decreased, and then elevated to his highest of the year. Minter is being beat out of snaps by a rookie SS who is playing ILB. That is a pretty bad sign.