Why might an 8-inch reflector yield less satisfying results than a smaller 4-inch refractor during poor viewing conditions?

The air turbulence itself becomes the limiting factor, overriding the large aperture benefit

When observing from locations afflicted by poor atmospheric seeing—such as instability caused by heat rising from surfaces or high humidity—the performance of large optical instruments can be severely hampered. In such turbulent conditions, the air distorts the image far more significantly than the resolving capability of the telescope itself. An 8-inch reflector, despite having twice the light-gathering power of a 4-inch refractor, will have its potential clarity limited by the shaky atmosphere. If the air quality is poor, the larger aperture simply collects more distorted light, meaning the smaller, higher-quality optics used on a night with exceptionally stable, 'glassy' air can sometimes provide a more satisfying and clearer view because the medium itself is less disruptive to the image formation process.