Sadly, the move from inline-6 to V-6 was a Schrempp-driven move rather than an engineering-driven move. The move to the V-6 was driven mainly by economics -- it is a direct descendent of the V-8 design and can be produced on the same line. This significantly reduces manufacturing costs over the inline-6 engines, which required a separate production line.

There are demonstrated advantages (in general) to inline-six designs over v-6 designs, in terms of smoothness. The knowledge that MB made inline-six engines for many decades I guess was given up with the demise of the M104 in the mid-late 1990s. MB inline-six designs have been proven over many years, despite some warts (such as the head-gasket issues, which were an auxiliary part design (materials) flaw as opposed to an engine design flaw).

Notice that today's V-6 designs don't offer significant (discernable) power or efficiency improvements over the M104 designs. Also note that V-6 engines with balancers tend to steal horsepower from the engine.

It is also telling that BMW still continues to manufacture inline-six designs for its cars.

My two cents.

Cheers,
Gerry