It is an apple to oranges comparison. Sounds to me nothing more than owners with high expectations of reliability and instead should buy a Toyota.

The W210 is an excellent car overall, with quirks just like any other vehicle you buy.

The W140 is an excellent car overall, with quirks just like any other vehicle you will buy in a lifetime. Both are so different the comparison isn't possible.

The W210 was a more affordable mid-line model so how could it be the equivalent to an S-Class?

Shoulda bought that S-Class then.