No defending Mercedes from me. I was a diehard MB owner, having had the following:
1987 190E 2.3
1987 190E 2.3-16V
1988 190E 2.3
1990 190E 2.6
1995 C36 AMG
1998 E300td
1998 C230
And logged over 1,000,000km on them.
Even the older MB's had issues, but not major mechanical ones. On the rare occasion (OM606 engine, one example) they would, MB stood behind them. Many of those six-pot diesels were replaced by Mercedes long after the warranty ran out.
Then came Lexus. Mercedes didn't take it seriously at first, but then began to lose market share. Mercedes could not figure out how to build a car to the Lexus price point without cutting corners. They couldn't add the gadgets Lexus had without installing poor electronics.
By the late 90's, the thick sheetmetal was being phased out. The super thick hides were no longer being used. The paint had become environmentally friendly, and thin and easily chipped. The electronic systems in the cars were overly complex and unreliable. My 1998 C230 was among the last of the "simple, robust" Mercedes models. The M112 V-6 engine had rivets in some spots instead of robust bolts, pointing to a new idea of "don't fix, throw away" at Mercedes. For shame.
To Mercedes' credit, they didn't understand the new luxury car buyer. Once upon a time, someone paying $40K or more for a car wanted a keeper. They wanted it to last a long time. By the late 90's, everyone was leasing, and didn't give a rat's ass about longevity, and weren't willing to pay extra for it. They were just getting a new one in three years anyway, so who cares?
Two years ago I sold the 98 C230. It had been an excellent car, providing reliable service and enjoyable driving. However, Mercedes' reputation had been sullied, and it would take a lot for me to go back.