2010 was when they started using motors from other (cheap) brands like Renault for a lot of models on big scale. Before that you could drive your Mercedes up to like 400,000 km and more and still get money for it or at least sell it to development countries to be used as a - mostly reliable - taxi for example. Been there, done that. Nowadays getting a newer model to 200,000 km before its "end" is the exception rather than the norm. And that's just their cost-down strategy on the motors ...
The Renault engines are used in the entry level cars like the A, CLA and B class. The kind of Mercedes used as taxis (E and S class) will not be impacted by that change.
Please share what you believe happened in 2010 to Mercedes to cause the flip from an ideal choice for taxis to this consumer reports ranking.