に限らず・のみならず: the difference
に限らずN2
Meaning
Not just, Not only… but also
Past papers
Tested once in past papers
Example
ラッシュアワーに限らず、電車にはあまり乗りたくない。
Not only during rush hour, but I don't really want to ride the train.
のみならずN2
Meaning
Not only...but, Not just...but, What is more
Past papers
Tested 2 times in past papers
Example
炭素繊維は極めて丈夫であるのみならず非常に軽いらしい。
Apparently, carbon fiber is not only extremely durable, but also very light.
How to tell them apart
「に限らず」: goes beyond the original limit to the whole.
「だけでなく」: the most general, fine in speech and writing.
「のみならず」: solemn written style, used in speeches and papers.