Mercedes quality really dropped from 1998 on. It's been well documented and the CEO of Daimler admitted as much in 2005. Many people fault the Chrysler acquisition but the problems were also prevalent in the legacy class vehicles manufactured in Germany.
Supposedly Mercedes has gotten better, but not where it once was. They haven't gotten better than mid-pack the past two decades when it comes to quality ratings. Getting worse the past few years.
The 2020 JD Power Initial Quality Study ranks them near the bottom, at 202 problems reported by owners during the first 90 days of ownership for every 100 cars sold.