I'm always careful when using this as a reason. its fine to look at the metrics, but I also like to see what conditions existed that caused the metrics to be bad. sometimes you see the cause, sometimes not.
in the case of Mixon, (for example) he was playing on a team with a bad O line the last couple years. then when his QB went down last year, the metrics for much of the offense was worse. teams took advantage of that bad line frequently and early down run blitz turns into a pass blitz if its not a run play and the backup QB wasnt always up to the task to make them pay for this.
hes in a far better place now where the run game will be more effective. Im not predicting an explosion of fantasy performance but I think he will be at least as good and likely a bit better than last year.
just food for your thoughts. you are not wrong about the metrics for the players you mentioned. but you should try to go one step further in your analysis. might lead you to some better conclusions