I'll start by saying that these people annoy me too, so I understand your frustration, and I see the parallels you draw with teams for favourites (and low-value content in general, e.g. gamefreak logic questions). However, I'm not convinced that banning them altogether is the best outcome. I actually think this is a perfect example of when you should down-vote a question.
The reasons I think this are a) the question is at least answerable, and b) I don't completely agree with the way you characterise them here.
These questions aren't helpful at all to anyone else and are not even helpful to the asker themselves.
I think it's a little bit harsh to say that the questions don't help anyone else. Sure, the exact question of whether Petal Dance is good on Roserade in AG is useless from a competitive standpoint, but I 100% believe people would click on that question if they wanted to know about RU instead, or whatever. The advice won't always transfer perfectly between formats, but I think it's enough that the question contributes something to the collection of answers on this platform.
I think it's flat out untrue that the question doesn't help the asker. Both of us know what they should be doing instead, but it's true that in both examples you gave, the asker came away happy with the answer. They also got some advice that I think will help them in the long term: "x Pokemon is more viable in y format, so you should play that instead". I don't always think these people are deliberately throwing games playing favourites -- they just don't know there's a better way of going about that. They go to AG because the name assures them they can play whatever combination of Pokemon they want.
To be clear, I 100% agree that questions which genuinely only service their asker should be heavily considered for a ban (especially if they're tedious to answer). But I don't think this is the greatest example of that.
I also agree with sumwun's point here:
I don't think the editors and moderators should be the ones deciding which Pokemon are viable in which formats.
Although I believe I'd personally be able to pick out questions asking about unviable Pokemon accurately, that won't necessarily be true for every staff member, now or into the future. I think we should avoid having a rule that depends on our knowledge of competitive Pokemon whenever it's possible. (I suppose we could just use stats and VR threads as a reference, but having rules that depend on what Smogon is doing sounds just as messy. Our rules should be within our control.)
It's true that we'd effectively be doing this in the RMT section if we added the new rules from the survey, but I do think it's easier to remove a whole team for lacking awareness than it is to remove one question asking about one Pokemon and one move. My opinion on that might change if we implement that rule and it goes well, though. (BTW you'll be hearing more about those rules soon-ish -- I don't have time to write big PokeBase threads for a couple of weeks.)
Feel free to give counter-arguments to this, what I say doesn't have to stand if it's wrong.