I 100% agree that the term 'alliance' as used on this forum has no consistent correspondence to anything beyond very general taxonomic relatedness. While this creates an ambiguity of sense (same word-sign, different but somewhat related meanings) with the term 'alliance' as sometimes used by taxonomists, there's never been any apparent effort or intent to use it in the taxonomic sense here.
I see many problems with segregating the current forums based on growing conditions or breeding efforts but probably not worth going into here. Personally I see nothing wrong with Glen posting an obscure but beautiful genus in a forum devoted to a loosely-related group that as currently constituted does include that genus, but if you don't like it then you always have the option of not reading the post, right?