That's not what I mean by equal. You seem really hung up on these issues of balance and equality rather than the concept I am getting at which has zero to do with those issues in the game.
I am talking purely about the perception of a new player approaching the game.
Thank you for trying to frame the entire conversation and say only your concern matters, but there are other concerns.
Assume they know nothing. All they want to know is, in that very moment (not the future) if they buy into the game will they FEEL LIKE they're not far behind. Right then, as they enter the game.
And at that moment, being asked to IMPLY there is no problem because there is a Core +1 Rule rather than being TOLD EXPLICITLY that they've created rules tailored to avoid the problem is not going to be inherently better.
Odds are once they get into the game these issues will go away. So future books are irrelevant, and the reality of balance and equality once actually playing is irrelevant. All I am addressing is the message in that moment to a new player about purely the perception of not being "behind".
AGAIN, no. Not true. Irrelevant means no relevance, and it is quite relevant to some players that they are prevented from taking certain options because they chose the wrong +1.
Again, entirely my point.
They don't want to hear about lots of options in that moment. That's not the theme of this edition anyway. And they're not going to read it in that moment either. They're saying to their friend or someone in the store "Hey, I am interested but I am worried about being behind and there seem to be lots of books" and the person can respond, "Don't worry, you can only use the Player's Handbook and one additional book of your choice anyway, like this latest one that just came out for example - nobody can use lots of books so nobody can fall behind or use some library of books".
Or they can be told, "No problem. Use the PHB to make a character. If there is anything outside the PHB you want to us, just check this list. You don't need to worry about using anything outside the PHB now - it has plenty of options to get you started... you'll likely want to look at the other books after you get going."
That's it. That's the moment of decision. None of the rest of this about preserving balance and preventing abuse and equality of footing and all that, none of it matters to that moment.
BUT IT DOES FRIGGING BELL TOWER OF BUBBA GUMP matter. And, as I've repeatedly said, there are multiple ways to address your concern that do not hamper the long term options in the same way.
Now of course a more complicated system with such an intro paragraph could be phrased by a responder in that moment in an appealing way.
I'm glad we agree....
But the more complex the answer the lower the odds the potential customer becomes an actual customer. This answer is super simple. Everyone gets it, and it's easy to understand. The complexities of the system you propose do not rival that simple answer.
I disagree with the notion that someone with no context for the game is going to imply the benefits you perceive more clearly than if they are explicitly told, "We got you, Dude. Create away."
The system you want is great for home play.
It is unnecessary for home play where the DM can craft whatever limits they want.
It's what I use, it's what everyone I know uses other than those who play in AL. But, for the optics of selling to new customers at the game store, the system they came up with works best I suspect. Simple is far better for that point of sale pitch.
OK, put all that aside for a minute.
Bob walks in the door. Bob wants to play. Bob asks how to get started. Someone, magically, Bob implies that at the moment of character creation he is on a level playing field with everyone else because of the Core +1 rule. Bob makes a character and plays 2 sessions with his Hexblade. Then, Bob hears about Eliminster's Manual of the Planes being released. And it is FREAKING AWESOME. It has perfect stuff for his PC. And Bob is told, "Sorry, you can't use anything in it for your character... you chose Xanathar's as your +1."
Does Bob like that he is told he can't use it?
Does Bob feel like buying a book he can't use?
Does Bob feel like the game protected him with the +1 Rule, or that the +1 Rule screwed him?
Any argument about the simplicity of Core +1 being a great selling point can be countered by good marketing of whatever alternative system you propose.
In a very real sense: The rule, in and of itself, acknowledges it is a faulty approach. If simplicity is the ultimate selling point, why not go even simpler and make PHB the only option at level 1? Much simpler. Balanced for time and cost issues. Balanced for power gaming purposes. Heck, why not limit players to just the basic rules options? Even simpler!
Why? Because we want to allow options more than we want ultimate simplicity. We want players to be able to use these new materials, and a rule that fairly arbitrarily groups things and says, "Hey, right now, when you know little about the game, pick from one of these pools, or decide you want to wait to pick one later..." is a turnoff that worries new players. I've seen it at AL events. The question of, "Should I play an XGtE class or just a PHB one so that I can XXX later" does happen.
Summary:
There are options available that offer a better long term gaming experience with more options.
Any optics advantage for that brand new player are suspect because they require inference, and are countered by negative perceptions that might drive them from the game once they start.
Done.
