> but naively choosing ffmpeg parameters can often result in noticeable quality loss

Welcome to the world of video compression. If you're not able to take the time to learn the ins/outs of how to use a codec as well take each incoming video's specifics into consideration, then you'll be needing to borrow someone's middle of the road presets. Dedicated settings make decisions based on the frame size, bitrate restrictions, things like HLS vs download/play, 1pass/multipass etc. All of that determines GOP size, reference frames, etc.