Those things are just as flawed as YPC. It's nearly impossible and virtually pointless to create these combined stats for football. As was said earlier, too many inter-dependencies.
That success rate stat is an interesting concept but it only tells a tiny fraction of the story. That fact is that a 17 yard run on 3 and 3 is much more 'successful' and impactful than a 4 yard run. Yet that particular stat values them equally.
Combined stats? Pray tell, what's being combined? Passer Rating is a combined stat. Things like Expected Points and Success Rate are as much a straight metric as yards per carry.
Also, you clearly don't understand the point about interdependency. It's what makes it impossible, at present, to isolate a running back's performance from that of his offensive line. It's what makes it take more work to tell the difference between a "bend but don't break" defense, and one that just given better mean field position.
You are acting as if these limitations make it pointless to compare relative merits of statistical metrics, when in fact, the exact opposite is true. You also are acting as if it's better to simply choose just one metric to consider, when you're argument about interdependency would strongly suggest that its better to look at a number of them in conjunction.
For example, Supafly brought success rate into the conversation not to replace yards per carry, but to add more context to what we're taking away from it. We know that some of the weaknesses of the yards per carry metric are that it doesn't take consistency into account, and that it's situation blind - i.e. a 15 yard run on 3rd and 20 is worth 3x as much as a 5 yard run on 3rd and 5.
So given two backs with equivalent yards per carry rates, the one with the higher Success Rate has gained that yardage more consistently and with more situational value.
Finally, if you have problems with interdependency, you should welcome the addition of Expected Points Added and Win Probability Added to the conversation. While they are no more able to discriminate between the running back's contribution and the O-Line's, at least they aren't hopelessly interdependent with game situations. Are they perfect? Surely not. Do they tell us more than YPC without adding any other unaccounted for variables? Absolutely.