One reads that so-and-so is a 'devout Catholic' or a 'devout Muslim.'
How would the writer know? Devotion is an interior state inaccessible to observation from without. The practicing Catholic or observant Muslim, by contrast, can be seen to be such by others. So if what you mean to convey is that so-and-so is a practicing or observant Christian, Muslim, or Jew, then you should write that. It is obvious that the practitioner of a religion need not be particularly devout or devout at all. And that includes priests, rabbis, and imams.
I grant that external practices are evidence of inner attitude. So, by the dictionary definition, you would not be wrong to call a regular practitioner of a religion 'devout.' But here at Maverick Philosopher our standards are a cut above those of a mere dictionary. We aim at precision in thought and speech. And sometimes we miss the mark.
So rather than bandy about, lemming-like, an oft-heard phrase, journalists should ask themselves whether the alternatives suggested above are more appropriate.
Language matters.
Speaking of dictionaries, The Dictionary Fallacy is a very good article in my biased opinion. It will cost you some effort, but a little hard work never hurt anybody.