We stayed at the JW last month (adjacent to the Casa Magna). The beach was great. This winter, they totally rebuilt the beach along the whole strip, and anyone saying the beach is bad is probably talking about last year when it was all swept away by hurricanes.
The attached photo is looking towards the Casa Magna from th JW - it was a cloudy day, but other than that, nothing wrong with the beach. The picture was taken on 2/18.