Perhaps the most overlooked feature of 2018.5 was . Remember when you had to delete history constantly to keep blendshapes from exploding? 2018.5 introduced a non-destructive workflow for deformation ordering that changed how character TD's thought about rigging.
Unlike the major feature overhauls found in initial releases, Maya 2018.5 was designed as a "service pack" style update, prioritizing hundreds of bug fixes to ensure production-level reliability. This made it a preferred choice for studios that valued a stable, predictable environment over the experimental features of newer versions. Autodesk Maya 2018.5
This is a tricky domain. Autodesk no longer sells perpetual licenses for 2018.5. If you are a student or professional: Perhaps the most overlooked feature of 2018