I also have a square trigger guard 1911 and I really do love the ARG DL, it is my #1 holster, I own more than a few of them.
Are you sure you were speaking with Mitch Rosen himself, If so I am really surprised he responded in that manner, I know the reputation that follows him on the internet, but I have always found him to be a gentleman and a very good business man.
Several years back I had one of the first P7M10s in the USA and Mitchell was the only person I could find with the experience and knowledge of the gun and he spent well over an hour on the phone with me on three separate occasions discussing the gun and his holster design thoughts. I then ordered two through a local/range store here in PA, they are really good holsters of very high quality.
Recently I have also purchased several pieces of Rosen gear through Terry Peters and I like it a great deal.
As to other makers, I think the guys have mentioned some really good ones and I am liking Lou Alessi's work more and more as I continue to see nothing but good things coming from his shop, Lou is actually helping me to develop the “right” holster for my N frame carry guns and he is easy to work with and very quick to pick up on what I am explaining in non-holster speak.