All your monsters don't have to be a copy paste of the MM you know. NPCs are better if their 'legal' but monsters should fit to every situation.
I mostly agree (monsters in the MM are just examples after all) except for cases where homebrewing makes them less interesting. E.g., Imps without DR are equally as interesting combat encounters, but Intellect Devourers without the ability to devour intellect...at that point they can only do a basic attack. Just use an wolf/imp/humanoid thrall enemy instead.
