Board Thread:General Discussion/@comment-25814498-20150505201606/@comment-27900912-20160305235750

Nen masters are able to use the other categories with ease. Whether this means they can use it at 100% at a reduced level or just means that they are so good that the reduced percent basically doesn't matter isn't known or shown, sadly. So all we know is that Nen masters are able to avoid/overcome Memory Overload.

Also, I believe it has been shown that Nen users generally have their primary Nen type and also lean towards a secondary Nen type, like Gon is an Enhancer and leans more towards Emission (instead of Transmutation).

But yeah, Meruem was just crazy naturally OP. He was the King, so he was already uber tough, and he was born able to use Nen, so that made him even tougher. Compare a human Nen user to a regular human, and the difference is huge. The comparison is similar for the Chimera Ants, plus higher up Ants are naturally better, like a bodybuilder vs a Leorio :P