Complex sentence: While Rolemaster does indeed offer many rules and tables, most of this content is strictly optional and intended to be used selectively; pick the right tool for the right job, rather than a "everything-and-the-kitchen-sink" approach.
Split into simpler sentences: While Rolemaster does indeed offer many rules and tables, much of this content is strictly supplemental. The intent is for the gamemaster to pick the right tool for the right job, rather than take an "everything-and-the-kitchen-sink" approach.