There are two problems with this ridiculously popular but baseless theory:
First, it IS possible to be corrupted by energy from multiple dragons at once. See: Crucible of Eternity.
Second, Malyck has no exposure to the Tablet and its teachings, and still behaves more like a Dream sylvari, or at least a Soundless, than a Nightmare Courtier or a dragon minion. This disproves the claim that the Tablet has significantly changed the nature of sylvari - instead, the Tablet is accepted because it's compatible with the natural attitude of most sylvari.
While I was at lunch with Colin Johanson on Weds, I had a brief chat with Aiden (the EU CM) re: this issue. he stated that the risk of scamming was the main factor behind it, but that if people who had been artists and customers in GW1 could PM me with their experiences (both good and bad) he would make sure this issue was revisited.
Basically, they need to be convinced they wont get a bazillion support tickets about being scammed by artists. So, hopefully given enough examples and testimonies we can change their mind. So while its not a dead cert theu will change their mind, at least they are prepared to have another look.