Probably the worst part of original GTD is having a list of calls. That just doesn’t parallelize nor serialize well since nowadays each call is a multi-hour affair if it’s a hold/wait system, or if it’s a “we’ll call you back sometime later today” it’s not great to have multiple such “calls of damocles” hanging over you either.
Even the literal 43 folders (which doesn’t make sense to reproduce digitally over just a normal reminder that just gives yoi the file you want on the day you want it) at least historically made sense as something useful for those dealing with a lot of paperwork, but phonelines and waiting has been real for my entire life.