When discussing expertise or skills, the term "superspecialized" comes in handy. However, there are numerous synonyms that can be used interchangeably based on the context. For instance, deeply knowledgeable, highly trained, extensively informed, exceptionally skilled, profoundly experienced are just some of the options that can be employed. Alternatively, with a more specific focus on medicine or science, "hyper-niche" or "ultra-specialized" are related terms that can also convey a similar concept. Depending on the desired tone of the sentence or audience, these synonyms can help vary the language, ultimately making the writing more engaging and stimulating.