Yeah, whether it's a legitimate workaround or not really depends on what you're trying to accomplish. If you're mostly ok with one of the base playbooks, and just wish it had like one or two additional elements, it works pretty well. At the same time, I also totally get the desire to rip a playbook all the way down and build something streamlined from scratch, you're probably only going to end up with about 50% of the forms you can sub.
Then again, I can't think of a time I've wanted to make form subs for more than a few formations here and there (a place to field a depth WR or TE to get them reps, for example).
Where I HAVE found a good use for it is with defensive playbooks when I have multiple guys at the same position that I want to use for different purposes, or when O want to run a true multiple front D, where I'll have pass rushers at both DE and LB, but also have coverage LBs I want in certain situations.
In that instance, you can use the specialist depth chart to your advantage. Like, pick a 4-3 defense as your scheme, add 3-4 front plays to it, set your pass rush LBs as the rush ends, then go manually switch guys back in the form subs you have access to...which will be the 4-3 plays.