Shifters are a preference at best, and a religion at worst (think Campy vs Shimano, or Retrogrouch vs Techie). There is nothing inherently better or worse about a set of shifters, just what you like.

That being said, most of the production bikes that came with stem shifters were of lower quality, so they do tend to correlate with lower quality bikes. However there is nothing inherent in their design that dictates poor performance, as Ahearne demonstrates.