I disagree with this. Why shouldn't I be able to go out on my 50THM and kill an NM for a drop to help me level another class? I like to be prepared and have gear several levels before I need it.

Bear in mind these are just the first few NMs, and mid-level ones to be introduced. There will be higher level NMs put into the game at some point which won't be an easy solo, or will require a party to take down and more of a challenge.
By putting in mid-level NMs (and hopefully even lower level ones at some point) gives everyone something to do- lower rank players can join together as a team to take them down, and higher rank people can still go and kill them for items.

I have to say even at rank 50 some of these NMs are still fun to fight and give a challenge solo- Phaia and Sirocco for example... as a mage they hurt!