To some extent this is a philosophical discussion about the utility of the 40-man roster in MLB circa 2019.
But in reality, the guys who are on the taxi squad are on the taxi squad for a reason. If they have a big league future, be it in the pen or as a starter, it will still happen for them. It might not be with the Phillies if their development line doesn't sync with the team's goals. Right now the question isn't whether Cole Irvin and Enyel De Los Santos should be starting, relieving or staying in one place, it is whether they can be traded for a better starter (especially given Arrieta's situation). And there's no scenario - especially with 7 relievers on the IL or whatever - where the minor league relievers can just be left alone to develop (or left in MLB to get lit up) exclusively.
Of course both of those things might change in the next three weeks.
I also think when things are going bad people naturally look at what's being done differently as the reason, but it's not necessarily the case. Also, our particularly minor league-centric board loves nearly everyone when they are still in the minors, and then assumes the major league club screwed them up. Gabe Kapler certainly didn't start that.
And this applies to what people think of his game management too. For all the hype about Kapler's unconventional methods or analytics, second-guessing the manager about staying with starters or overusing relievers hasn't changed in my lifetime (or the Internet's lifetime, I was never much for radio). And whatever he is doing that is truly unconventional, the next manager would do it as well, because that's how these front offices work now.
I'm also with Fla, to call these days when AAA pitchers get 10X the salary and credit towards their pension "abuse" is a big stretch. Most of the guys who have come up and down have done so on merit. In 2019, bullpen "swingman" is just another job like pinch-hitter or utility glove (or "closer") and for some people that will be their ceiling. Arano rose above it quickly. Ramos has mostly been sent down because he needed to pitch better, not because they needed to churn the arms, and that's been going on since Mackanin was the manager (him specifically, I mean).