When it comes to expressing the idea of "fails heavily", there are a number of synonymous phrases that can be used to effectively convey this meaning. Some other terms that could be substituted for "fails heavily" might include "falls short", "misses the mark", "comes up short", "strikes out", or "falls flat". Alternatively, one might opt for a more creative phrasing, using something like "crashes and burns", "bombs", "flops", or "flounders". Regardless of the exact synonyms used, the most important thing is to choose phrases that accurately capture the idea of something that has failed in a significant or decisive way.