I agree. And as a DM, there's just as much chance I'll let you use that elephant with plate barding at my table as I would let you use a half-dozen simulcra (each of which created another one) to overwhelm my adventure. That is to say, zero chance. That is the authority AL gives me as a DM ("A DM's ruling at the table is considered final for the purpose of that play session."), and that is *especially* true if you're going to be a jerk about it.
The difference is, if you write down that you spent gold and downtime days to copy spells from a spellbook, and list the spellbook under the treasure for the adventure where you got the spellbook, I can take a quick look and say, 'OK, that checks out.' If you mis-record some of the spells, I can tell you to correct them, or if you refuse, forbid you from using the spells that weren't actually in the spellbook you claim to have gained.
If you've got an elephant, though? Where are the records of you feeding it, or if you're going to argue that you're feeding it with your lifestyle, why are you still sitting on the Modest lifestyle from your original background? Where do you keep it? How did you get it to Mulmaster from Phlan? Give me a good, interesting, rational explanation for all this stuff, and sure, I might be persuaded. But the point is, as others have already pointed out, that AL is not a venue for anything a player can dream up. AL is about getting together and telling shared stories around the gaming table. Anything you put forward that gives me the idea that you're not planning to share, and are instead going to hog the limelight and troll my table for the lulz, is another reason for me to make as full a use of my authority as DM to stop you from ruining the game for the other people at the table, each of whom is just as deserving of having time in the spotlight and feeling as though they have an awesome character as you do.
I don't expect players to try to police each other -- if the players are threatening each other to keep the adventure on track, I've already failed as DM.
If this means you're uninterested in playing Adventurers League, because you suddenly realize that every DM you play with isn't just going to trust you so that you can pull of whatever shenanigans you feel like pulling, then I for one am breathing a heavy sigh of relief, for my own tables and all the other tables that won't be wrecked by a selfish player who uses the rules as a bludgeon to beat the fun out of what should be an entertaining pastime.
My god you're a bad DM. I don't mean in the sense that you don't know the adventure or keep track of mechanical aspects, it's just blatantly clear that you view the players as the enemy and them beating "your" monsters or override your "authority." I feel really, really bad for your players.