In particular, the harmonic mean's practical use is mainly illustrated through 'average speed,' and the explanation typically ends there.
Literal
Especially, harmonic-mean [possessive-の] actual use-examples [as-としては], 'average speed' [subject-が] mainly taken-up, explanation [subject-が] there [at-で] ending [topic-は] standard-practice [copula-である].
調和平均 ('harmonic mean') is the math term. 実際の使用例としては ('as for practical use examples') frames the scope. 取り上げられ ('is taken up') is passive. 通例である ('is the standard/convention') closes with a formal assessment. The sentence criticizes the narrowness of typical textbook coverage — a meta-pedagogical observation within a math text.