Psychological depth in Tolkien's characters

[Aiwendil]

Eurytus wrote:

A character can be powerful but poorly defined with no psychological depth. Sauron after all is powerful and in LOTR you see absolutely nothing about him.
To a lesser extent Glorfindel too is portrayed as very powerful and again you do not get a good insight into his character in my view.

I think that what Lindil meant (if I may be so bold) is not that powerful characters automatically have psychological depth, but rather that the fact that the character is powerful is one of the pieces of characterization that goes toward establishing psychological depth.