The problem is that while units were formed in previous wars for special purposes, they didn't last, and most definitely were not commonplace in any army in the 1930s, which is where the criticism comes from. Far too modern (not to mention awfully commonplace even for a modern army). If you look at the official history of the 75th Rangers (see here:
http://www.soc.mil/75thrr/75thrrhist.html ), you'll see that while they take certain things from their long-ago predecessors such as Roger's Rangers of the French & Indian wars, there were no such units in the US Army during peacetime until after the Korean War (and, even then, they only became a permanent part of the US Army's TO&E in
1974).
Once war breaks out, sure, some of these units get formed, but most armies will be lucky to field a single regiment for their entire army (quite likely as separate battalions or companies rather than under a single regimental headquarters).