I don't think you're giving enough credit to the players they did try, like Schaeffer, Mastroianni, and Robinson. Sure, as I type them it seems ridiculous as neither of the three amounted to much, but hindsight is 20/20 and I really don't see how Walker was that much better of a prospect than these three. If Mastroianni had been stuck in AAA while they tried Walker, and Walker hit .100 while striking out in 55% of his at bats, we'd all bemoan the fact that we never gave Mastroianni a chance.
Now I can't prove that Walker would have hit .100 and struck out in 55% of his at bats, but you have to compare apples-to-apples. You can't say "but Mastroianni had a .573 OPS", when prior to deciding which one to call up you don't with certainty what either ones OPS will be.You have to look at each player, the skillset they bring, and the likelihood of success in the bigs.In my opinion Mastroianni was just as likely to have success as ABW.
1. Darin Mastroianni got chances with the Twins in 2012 (.678 OPS), 2013 (.444 OPS), 2014 (.083 OPS) but was waived and Toronto tried him out (.406 OPS). After a bunch of different tries, he ended back with the Twins in 2016 as a 30 year old (.182 OPS).
2. Was Darin Mastroianni this great minor league player? Hell no. Walker hit more home runs in a season than he did in 10 minor league seasons.
But yet, the Twins kept giving him a chance without giving a better minor league hitter a chance. While I don't think it would make a difference, it was a certainty that Darin Mastroianni was NEVER going to develop and the Twins gave him chance after chance.
So, again, I repeat, how they handled this specific situaiton was just a symptom of why the previous front office could not turn the team around. THey kept plugging in the same old mediocre at best players rather than committing to prospects at the major league level.