When it comes to reducing something, it is often important to strike a balance between making a meaningful impact and going too far. If the reduction is too great, it may result in unintended consequences or negative effects. Some synonyms for "too great a reduction" include excessive decrease, disproportionate cut, drastic lowering, and extreme reduction. Additionally, you could use phrases like "overwhelming reduction," "significant drop," or "radical shrinkage" to convey a similar sentiment. It's important to carefully consider the context and desired outcome when choosing synonym or alternative phrasing to describe a reduction in a given situation.