To be clear, there are two issues here. One is "no blackout dates" which means "no rooms available." There is little evidence that legacy Marriott hotels are making zero rooms available. The other issue is capacity controls. Legacy SPG had "if you can book a standard room with cash, you can book it with points" so no capacity controls on standard rooms. Marriott advertised that this would be the policy with legacy Marriott brands as well. But then had to pull back because the hotel owners pushed back and the agreement between Bonvoy and Marriott owners did not force this on hotels. So legacy Marriott is once again allowed to have capacity controls on standard rooms.

As an example, if there are 10 standard rooms in inventory to be booked with cash, then legacy SPG hotels have to offer all 10 for award redemption. Legacy Marriott brands just have to have 1 of those rooms available for award redemption to satisfy the "no blackout date" policy. And if that one room allocated for point redemption is taken, you will get the "this hotel is not taking award redemptions at this time" error even though there are standard rooms are available to book with cash.

The lack of capacity controls was a huge selling point for the SPG program and was highly touted as something that Marriott would roll out across the entire combined chain. Having to pull back on this is a big big devaluation vs what was promised.