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That may be true if you expect to progress straight to a big shiny jet, but smaller airlines operating turboprops may still be interested in instructional hours.
What they won't be very interested in, unfortunately, are instructional hours spent at PPL level - anyone aiming for an airline career needs to be thinking about IR and CPL instruction as soon as the chance arises, and even if a flying school wanted to bond you for multi time or instructor ratings it is immaterial, as the pay rise you get going to the right hand seat of almost any airline would make it easy to pay off the bond.
Back to the original part of the thread, I spend a lot of time instructing sitting with my arms crossed, and have done for the last twenty something years - if you sit in a C152 there really isn't any other comfortable place to put them and it doesn't mean you aren't fully alert - after all how often do you actually have to grab the controls to save yourself, rather than just advising the student how to recover from the situation they may have got them selves into? (I am not advocating this for a students first few attempts at landing when you may want to be a little closer to the controls, of course).
If mystery shopper is correct that the article suggests that training as an instuctor is a bad thing for those looking for a career in aviation then surely that is a good thing for career instructors. Less frozen ATPL holders prepared to work for peanuts means better salaries - eventualy - for those who want to instruct.