A friend of mine who had extensive charter experience was told during her interview that said airline would prefer she go back and use her grade 3 instructor rating to get some more valuable aviation exposure prior to applying again...
That sounds more like a "don't call us, we'll call you" using a small insignificance to let you down lightly, rather than say, you're just not our thing at the moment. That being said with the uncertainties around part 61 and whether trainers/checkers need instructor ratings airlines were hedging their bets and taking qualified instructors just in case. Instructors can have some insight to multi crew operations and dealing with cross cockpit conflict, all depends on where and who you have worked for. A pilot with just mostly VFR charter can struggle with the IFR component as would a grade three instructor with similar experience, maybe that's what they meantby broadening the experience base.
As for the ATO bashing, most I know are very experienced pilots with a varied GA career, not just instructing. Get to know your ATO, they are good people, and it will make checks a lot easier if you get along with them.