Yeah these sorts of speculation-fueled handwringing stories are total clickbait.
Like, the idea that SPG members are some sort of high-class sophisticates is pretty dumb on its face. The idea that "marriott people" are going to "overrun" SPG properties and "SPG people" are not going to do the same with marriott properties is also pretty dumb.
I mean, if we're just going on bare speculation and don't have to provide any data... Usually that particular objection is specifically brought up when it comes to lounges. SPG grants lounge access with a much smaller level of effort from the guest (as few as 25 nights!) so I would think a higher percentage of SPG crossovers would be sampling lounges than the opposite.
The funny thing is that the deal docs make clear that the main basis for the transaction was that SPGers were spending lots of nights at random lower tier properties ... it was an extremely high percentage relative to Marriott ... so by buying Starwood, Marriott could get the "SPGers" to stay in Courtyards and Fairfields that than HGI/Hampton Inn/Hyatt Place/etc.