Complex sentence: This niche was, at the time, dominated by Sturm Ruger's well thought of Mk I and Mk II series of pistols and was a market position S&W had neglected since 1966, when the model 46 was dropped from their catalog.
Split into simpler sentences: This niche was, at the time, dominated by Sturm Ruger's well thought of Mk I and Mk II series of pistols. Smith & Wesson largely neglected the market position since 1966, when the Model 46 was dropped from their catalog.