Just back from a week at El Faro, on the beach, south side of Calle 10. Fourth visit to Riviera Maya (Cancun, Secrets Maroma Beach, PDC twice). I'm not applying for Destination Expert status, so I didn't bother to walk up & down the beach from Benito Juarez to Calle 40 & beyond with a tape measure, so take this report for only the area in front of El Faro, plus as far north & south as my eye can see.
Yes, there's sargassum every day, with a strip at the shoreline ranging in width from 2-5 ft. I easily stepped through it and into the water, after which there is more sargassum below the surface, up to about 15-20 yards from shore. After that it's clear sailing, although in dark water. It's a completely sandy bottom & warm water, and I could probably go out at least 1/4 mile before it's over my head.
WEATHER The forecast for our week was 80-90% chance of rain every day. The reality: it rained one day -- the other days were dry, so we spent each of them at the pool/beach.
Re sargassum cleanup: The day we arrived was the heaviest accumulation of seaweed. There were 11 workers with shovels & rakes in front of El Faro moving it into piles on the shoreline. By late afternoon they had built 6 piles about 4 ft. tall, after which 3 small front-end loaders arrived to make repeated trips to scoop it up, and transport it to the south out of my sight.