I would not challenge it directly. As someone who has come from faith to unbelief, I used to say such a thing. However, asking questions about it may help. My faith became shakier when I began to realise I was not as grounded as I thought. Too many horrible experiences a the hand of other believers, too many harsh realities of life that seemed to clash with the christian world view, etc.

“Excellent, that is a valuable commodity with the insanity of the world of late.”

Grounded in what?

Someone could just as easily say 'My Little Pony' keeps me grounded.

I would point out the contention "faith keeps them grounded" is an oxymoron for a start, unless they are willing to accept unorthodox definitions of three of the four words contained therein.