The book itself.
Good rule =======> get in the book.

Bad rule ========> Not in the book.

Flagship rule =====> Not in the book. So =====> bad rule.

If you don't want understand that... The only fact are the above.
And good or bad is not based on preferences of this or that person. It is based on game balance. Some of the rules of TCoE are not to my liking but I must admit that they are not disruptive. Distasteful, yes. But not disruptive at any table. But very very distasteful to me.
So, you have no evidence. "It isn't in the book so it must have been bad"
Zariel's Sword wasn't put in this book. Must have been a bad item. Ring of Winter wasn't put in here, must have been a bad item as well.
Shifters and Changelings weren't reprinted. Must have terribly designed races. Same with the Loxodon and the minotaur.
After all, we have spells and options from other books, even specifically from Eberron and Ravnica in this book, but those options weren't inlcuded so they must have been bad rules.
Do not assume what I think of you from what I think of your arguments. This is not related to the discussion.
Actually, I was referring to one of the things you said about me in your post. Your assumptions seem to be buried so deep that you might not even realize it, but I found it quite amusing.
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It is one rule. The rule as presented in UA was bad, and as such should not be published. It is in theory possible that in future they could come up with something a bit similar, but more restrained. If they do, we can evaluate it then.
So, no proof, just your personal opinion on the rule. Nothing else.
This is obviously wrong. Wizards are more powerful casters than bards due their better spell selection and ability to swap spells and this is balanced by bards getting shitton of more stuff than wizards on top of their spellcasting. Furthermore lore bard gains access to more spells as their sixth level feature. Other colleges get something else at this level, such as the extra attack of the valour bard. Access to extra spells is obviously considered a beneficial feature that uses up part of the subclass 'budget'. Land druids have a similar deal. I literally cannot believe that I need to explain this to you.
And so when the wizard got more spells in Xanathar's and Tasha's the bard got things to compensate for the wizards increased power?
And, the Lore Bard didn't get other features, like cutting words, which might act as part of their power budget? It is only about the wizard having a bigger spell list?
I don't know why I'm bothering to ask, you are never going to change your position on this. I've provided all the evidence I feel like putting into this.