My major point is that retailers will NOT accept this card by...

My major point is that retailers will NOT accept this card by default just because they accept Mastercard. This card will come with its own contract with its own transaction fee(probably much higher than existing credit cards) and retailers will be hesitant accepting it just like lot of them do not accept AMEX/DINERS due to their high transaction fees.

Now, as per the AfterPay research, 65% of millennials in US don't own a credit card, means they don't like the idea of getting into credit and paying fee and interest etc. Apple card is cool, however comes with an interest without any interest free period. You don't pat late fee, you just pay more interest with late payments(brilliant, today's generation is way smarter to understand the intent)

Moreover, this product will only be available to apple users(less than half the general consumers)

All in all, I think these are two different products, there may be a slight overlap but apple card is another entry in credit industry and a competition to existing credit cards more than BNPL players.

Just a small statistical fact if it matters: By the time Apple card is launched(this US summers), AfterPay will have more than 5 million active users(2 million US alone), hopefully some in UK too.