Here's the rub: if you use a debit card, the burden of proof is on you to prove you did not make the transaction. With credit cards, you shift it to the merchant/bank.

Firstly, that's just conceptually stupid, but ok, whatever, it's the US.

More practically: this is still a dispute process. You still have to fill in forms, you still temporarily don't have your money, you still might not get it back. Why take that risk when you could just have a popup on your phone that you click "allow" on? 15 seconds max.

You don't fill out forms or what you imagine. And because it is a credit card, you don't lose your money.

Regarding your last question, about the 15 seconds friction, you should work for a bit in online commerce to see how fast people give up paying if there's even a little inconvenience in the checkout process and go somewhere else they perceive it makes their shopping experience easier. The biggest drop in conversion rates happens at the checkout stage.

Where else would they go? The 3DS process depends on your issuer, not the merchant, so the process is the same no matter where you shop.

That’s a common myth, but is simply not true; neither practically, nor legally.

Both chargebacks and zero liability are practically available on effectively all US debit cards.

Legal protections might be a bit less than for credit cards, but still far from “you have the burden of proof”.

But your money is held in limbo until the dispute is resolved, right?

I believe only until the bank does some initial plausibility checks at first.

Actual dispute resolution can take quite long and you’re not even directly dependent on the outcome. For example, if you lose a card and it gets used in a physical store fraudulently, your bank will most likely not be able to win a dispute, but they’ll usually still have to reimburse you.

The thing that matters to you as the cardholder is only fraud liability; if and how your bank is made whole by the merchant is their concern. That’s the same across credit and debit.