Archie Struthers is probably a pretty good modern candidate.
But the old timers best known as One Hit Wonders which includes Crump, Wilson, Fownes, Leeds is a little misleading in a number of ways.
Those men weren't just one hit wonders--they were all men who were amateur architects (never taking money for what they did).
Why were they so-called amateur architects who never took anything for what they did? Because amateur playing status was much different than it is today in relation to architecture. In those days you couldn't take money from architecture and maintain your amateur playing status. And all those four, also including George Thomas (not a one hit wonder) and probably Max Behr, and certainly C.B. Macdonald had plenty of money and didn't appear to care about not getting paid.
But the thing that separated those particular so-called amateur architects and the courses they did from the rest, even including almost all the courses of the professional architects is that those men spent so long on the one (or few) courses they did.
That appears to be the key similarity to their successes. But if you look closely at all those listed they all appeared to have the courage of their own convictions to do the things in architecture they personally felt was right without any fear or concern about what others thought about what they were doing. This definitely was true of Leeds, Macdonald, Crump, Fownes, Thomas, Behr and perhaps to some lesser degree with Wilson.
In my opinion, these men proved beyond any doubt whatsoever that one does not need to be a professional architect to ultimately do great work in design. Matter of fact, the complete independent thinking of those so-called amateur architects listed compared to what most professionals had and have to put up with vis-a-vis clients may have been the best reason those men could create course like Myopia, NGLA, Merion East, Pine Valley, Oakmont as basically their first real efforts in architecture. They basically didn't have anyone to tell them what they couldn't do!!
Today professional architects all seem to be too concerned about somebody's negative reaction to something and that appears to be not at all the case with that impressive group of old timer amateur architects.
Plus all of them literally spent years with their course architecturally and otherwise, sometimes up to ten or more years and that's probably the thing it really takes that no professional architect I'm aware of has the time or the inclination to do.