I wouldn't say it severe no purpose other than bureaucracy, waste and limiting competition.

My understanding was that the 3 tiered system came about as a method to closely monitor and control alcohol sales. For example, medicinal brandy was still legal during prohibition and much of it was diverted for recreational use. Tightly controlling manufacturers, distributors and retailers helped keep that sort of stuff under control (kinda of... not really).

I don't disagree that it serves a very limited purpose now.