It also assumes the diety doesnt have people for that stuff. I personally like the old 1ed way of it. 1 to 3rd are prayer books. Any cleric can memorize from prayer books. 4 to 7th lower level to higher level followers of the dirty , administrative Angels etc. 8th and 9th level the diety has to grant directly.It's probably more like a "floodgates" argument than a slippery slope one.
Personally, it seems to me that if a deity can cope with all the clerical prayers for spells every morning, a little bit of Communing hardly seems like it will bother them.
Or to come at it another way: if a GM wants to veto the use of divination to assist in draws from a DoMT, then I guess that's their prerogative. They can even lampshade it if they want to - "Sorry, your god makes it a point of principle not to answer those frivolous questions." But trying to argue that fictional coherence strongly suggests, or even entails, that those questions can't be answered seems hopeless to me: gods have exactly as much capacity for attention and cognition, when it comes to noticing and responding to prayers, as the GM deems them to have.
I don't remember anything in any version of the Augury spell that says that the GM can use it to provide the player with false information on a success.
In the AD&D PHB it refers to "The base chance for correctly divining the augury". In 5e D&D, it says that the DM choose the omen based on what the results of the action will be. I don't have the 2nd ed AD&D or 3E wordings, but I'd be surprised if they said that the GM can just decide to give a false answer while presenting it as a true answer. I mean, in that case what would even be the point of the spell?