What it means
AもさることながらB means that A is notable or important, but B is also notable or important, often with greater emphasis placed on B. It is normally attached to a noun and is followed by a second noun or noun phrase, frequently marked by も. The expression is formal and is common in written evaluations, reports, presentations, and careful speech.
Usage note
AもさることながらB has a formal, somewhat fixed style and can sound too stiff in casual conversation. It is often confused with simple additive expressions such as AだけでなくBも, but it more strongly presents A as an acknowledged point before highlighting B.
How to use it
この製品は、価格もさることながら、耐久性も重要です。
For this product, durability is important in addition to price.
この製品は、価格もさることながら、耐久性も重要だ。
For this product, durability is important in addition to price.