This seems plausible, the call center quality definitely fell off a cliff before the merger in August last year. The call times went up drastically. We also saw people exploiting the situation booking 5 day travel packages despite not meeting the requirements, which seemed odd to me since Marriott appeared to stamp this out some years previously.
I think there is some evidence though that they are trying to respond. For example: My missing stay requests have been processed far faster than the 2 I had to do in 2016-17. My perception is wait times have improved since August last year. This is no where near where they need to be, but evidence of something.
I find it astonishing that the CEO only recently visited a call center for the first time. Hopefully that executive attention will drive better results. In my profession I have had to remediate a situation like this for a line of business in another Fortune 500 firm (although not to this scale). With the right executive backing you can move quite quickly to prioritize the right IT fixes, update processes, rollout better training etc, whilst establishing the A-team to clear the CRM backlog. Hopefully that is already happening or about to happen.