Except Xenoverse does continue the story and was even advertised to establish "the future of the Dragon Ball world", so that whole point is moot.
How does it continue the story in the same way GT does? GT was made to continue it
, in a way most fans would know of the continuation - as Dragon Ball, while having videogames is mostly known as manga and anime. The entire "establish the Dragon Ball world" sounds very much like simply an expansion of the franchise for me, not taking actual continuity into consideration. If that is really Toei's intention so, then so be it. But it does not reall sound like that any more than Star Wars also expands a world and in the end is worth nothing for the actual continuity.
Even then, it has nothing to do with the fact that there is an official stance regarding GT's relation to the overall continuity from an official product.
Which product? The videogame? If the videogame cannot be taken seriously then it very well is important to say that it cannot be taken into account.
Neither the anime nor the video games are created by the author of the original medium from which Dragon Ball was established (that would be the manga), so why does the anime suddenly have more authority than something like Xenoverse when neither one of them are directly associated with the source material itself? That doesn't make any sense to me.
It has nothing to do with what an author makes or not. I can pretty much refer to my first answer when it comes to that. When Dragon Ball ended in 1995 people mainly knew it as a manga and an anime. Even today that is the case. GT was made with the intention to continue the series - even brought Akira Toriyama to the (while he was just joking around, but at least) statement that with it existing he might continue the manga. Have you ever seen a game in all those years apart from Xenoverse that has actually had the intention to at least hint an actual connection? I didn't. So the doubt about a game being taken serious is very much justified while the anime is the main material - after the manga - from which we at least know that they intended to continue it. I seem to repeat myself but that is very important.
In general, this is exactly what I mean by selective reasoning. "The anime isn't the source material but it's valid because it's official" isn't consistent with "This video game isn't the source material and somehow it's totally invalid despite also being official because reasons".
As mentioned, it has nothing to do with being selective. You cannot just generalize things that seem similiar to you when in a certain context some important differences have to be considered. Just as you mention "not being created by the original author" yet you directly refer to something in a video game which you think to state something as not canonical. That is selective. You take into consideration how important the author's word is - even more important from what I read, but maybe I just misread - but then once Xenoverse is mentioned, Toei's word is enough for you. The entire part where an anime exists to continue the story where Battle of Gods was said to take place before GT and all that stuff does suddenly have no value to you. I do not about you but I do not think that is fair because if I'd actually knew, something neither I do, nor you, that Toei really made Xenoverse as a statement, then I'd accept it. Everything else is premature conclusion - because, while you are so convinced about GT having no relevance, what would you actually do when Super connects with it? Forget your thought "It won't", what will you do then? Not accept it?
I, for my part, can when Toei actually one day answers a question and says "well, GT no longer is part of the same continuity" - and we know it is meant like that and not just a thought of fans - then I'll be the one to say "oh, well, unfortunate but okay". However, will you do the same thing when the exact opposite happens? Or will you react like people did when they saw Super Saiyajin Gohan and claimed it to be impossible even though his possibility to transformed was even stated in vol. 41 but just ignored by fans who saw Gohan in GT - and Battle of Gods (not to mention that they can write whatever they want anyway)? This is being selective. Ignoring stuff that should be considered in the same context
. Not some videogame that was never announced to bring all official answer that we ever wanted and which should suddenly be taken as serious as some form of main media like manga and anime when it comes to story. I just want some fairness. Why don't you just wait for what happens?