Churches
People can follow in as many of the gods as they want – be it none or all six. They are not limited to one god, and those following a certain profession are not forced to follow the profession’s patron god (there is a necromancer in DR who in idle conversation complains Grenth is too morbid for her likings).
There are no “churches” by that name as far as I know, but there are monasteries and temples. Those mainly use the term temple.
And bringing all six gods under one roof has been done – Temple of the Six Gods was one such temple before the fall of Abaddon. Temple of the Ages was another (though originally for Grenth, it grew to five then included Kormir after her rise). Then you have the Shrine of the Six in DR though just a shrine and not a temple, it’s still under one roof (in one room no less). And there’s Serenity Temple in now-Blazeridge Steppes (though there’s only statues to Dwayna and Melandru, all gods were worshiped there, except possibly Kormir due to timeframe). In GW1 there was also the Chantry of Secrets in Elona (not the one in GW2), and Zin Ku Corridor.
Stop treating GW2 as a single story. Each Season and expansion should be their own story.
Can always count on Konig to get your answers here!