You're assuming that the Abyss came into being after the arrangement of planes in aligned structure instead of before.
It's more likely the other way around IF going by the clues in official lore across editions.
There was no "before". The Abyss was formed BY the Shard of Evil. The Shard of Evil itself was tossed into the Elemental Chaos, then started warping reality to form planar layers.
It's worth noting that the DnD cartoon realm doesn't actually have to be a region of Faerûn to be IN Faerûn.
A powerful wizard, deity, or godlike being might construct a realm inside a magic object, miniaturized so much it might even fit in the palm of one's hand.
I love DnD, but I chose "negative" in my opinion of its direction because it won't truly be "One DnD" unless they consolidate the lore across editions instead of retconning during every edition while putting out inconsistent red herrings.
I'd play a 1-shot or limited campaign with just 5.1 SRD, but as a wizard main who loves designing spells, I wouldn't commit to a long campaign that restricts me from something that I really enjoy.
It's a big extreme leap to make it a yes or no question when there may be infinite potential ways to make rules for and regulate AI through carefully considered laws.