I have only been into one Cabelas store and the staff in the FF section was very knowledgeable and very familiar with products including those not carried by Cabelas.

I have been into several Bass Pro shops and encountered staff limited and extensive knowledge and everything in between.

You get a wide range of experience levels at the big stores, which by the way, I have also found at smaller dedicated fly shops. Not everyone employed as sales staff in sporting goods stores or even dedicated fly or tackle shops invests the same amount of their time learning about all the equipment available and techniques for employing that gear.