Two Sets of Rules, the Good and Bad?

[OldTrees1]

I don't see a distinction between that perspective and "arguing that a DM should never use PHB rules for NPCs". What difference do you see?

The difference is:
One perspective writes a paragraph in the Monster Manual about adding class levels to monsters. Then writes 5 pages of support for the better / easier method.
The other writes a paragraph in the Monster Manual telling you monsters can't have class levels. Then writes 5 pages of support for the better / easier method.

Basically they know their style, but are they shutting down the other style, or still including it just in case?