But you won't. Nobody will, because it doesn't make sense. It's akin to saying, "I'm going to take the Magic Weapon spell, and then only adventure with groups that already have all magical weapons to point out how useless the spell is."
This is the relevant point -- the question is, regardless of the actual degree to which the rule is being used, is the rule perceived as unfair or inconsistent with other rulings?
I think there might have been one other person on the WotC boards at the time the ruling was announced who agreed with me that it seemed inconsistent, and you're the only person who seems to be arguing that it's unfair. At the moment, it doesn't look like there's a huge perception that this is a problem, so there's no urgency to 'fix' a problem that doesn't seem to be a problem. Honestly, even from my own perspective, I'd put a number of other issues higher on my list of things I'd like to see changed before I'd start heavily lobbying for this one.
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Pauper
I will admit I'm a tad unfamiliar with AL in total. I know a bit of how it works but haven't yet sat down to a table (life's a little tumultuous right now, and I don't want to commit to something I can't always make). However to my understanding I could take the same character from one table to another and do just what I said. If I offer spells to another wizard, in exchange for spells I don't yet have in my spell book, which of those wizard's is going to turn me down? From my understanding I'd have to spend two sessions with that party in order to legally trade spells. Unlike bringing magic weapon to a party that has nothing but magic weapons giving a wizard spells they normally couldn't get or just don't have yet is always going to be useful to that wizard.
The only reason I say it is unfair is because they get to make combos that other casters might like, but can't because of the AL ruling. It is literally the AL ruling that basically says the wizard and tomelock are allowed spells from any supplement ever while all other casters must specifically choose the one book they will use in addition to the PHB. Thats a level of freedom I'm not even sure I'm comfortable giving in my home games considering the absolute ruling from WOTC that supplements will only be balanced in relation to the core three books and not to other supplements (a perfectly reasonable approach considering a long publication cycle filled with many supplements).
To get a bit deeper into how AL works (because I actually do have some interest in becoming involved but am also riding the fence); could I take a character built with the scag and play in one season then transition that character to another season? If yes that means I could carry all of the scag spells (and any EE spells I picked up along the way) to another future season that had yet another season locked supplement and start mixing EE spells Scag spells and this new season's spells in a manner in which even WoTC hasn't anticipated or designed for.
In my personal opinion I'd say make it one of the two either all casters have universal spell list access or you have to choose your supplement and that limits the spells you are even allowed to pick up into your spell book.
Again this may not be the biggest deal. It may be an edge case, and there may be more pressing issues. I'm just saying it is rulings such as this that makes me wary of getting involved with AL. Because it seems like they make snap judgements and toss down a lot of banhammers on some mechanics while leaving a gaping hole in the entire AL system like this one totally alone and clarified as okay. All of this without even looking into things like specific mechanics (such as green flame Blade) as to if they are fixes for previous issues within the base D&D system (Blade locks being better off never using their Blade). They try to make the quickest sweeping judgments they can and take little effort to notice nuances that require more fiddly rulings and investigation. I know fiddly rulings are something the base D&D system is trying to avoid, unfortunately AL must be filled with a million fiddly rules for the sake of table consistency so the fact that they wouldn't take such a step for these cantrips is discouraging to me as a perspective player.
I know I'm somewhat unimportant in the grand scheme of things, and that it really doesn't matter if i want to play AL or not I'm just kinda tossing these things into the ether that is the internet because it seems a useful identification of an issue. If I'm wasting time here feel free to let me know.