Do the above mentioned airlines *really* think low hours f(ATPL) candidates, trained outside of an "approved" organisation are a training/employment risk
Yes, they do believe they are a training risk. Rightly or wrongly so, that is the experience that many of them have had - people who are capable of type rating in the minimum hours with minimal retraining are more likely to have come from an integrated background. The ability of modular students to work at their own pace - even if juggling jobs - is different from being forced to work at the course's pace at the same speed, a not so different environment from line training. That may be incorrect in many people's minds, but a more guaranteed product is lower risk that having outliers from modular backgrounds in their minds.
That is all fine, but what they are doing is discriminating against a certain kind of human being. No other industry behaves in this way. In other industries you would get a job interview regardless of how you gained your accreditations or experience
I am sorry, but that is simply not true. Some employers will not touch you unless you are an Oxbridge graduate; many investment banks have a list of top ten universities and those are the only from whom they recruit. Many jobs in accounting require training with Big 4 only.
Perhaps you could compare it to the argument that all degrees are alike, be they from Cambridge or Liverpool John Moores. Although some people at the latter may have worked very hard, the Cambridge degree will always trump it.
It all comes down to giving yourself the best shot you can - even if you are the exception, both ingrained beliefs and past experience have lead many airlines only to consider those from integrated backgrounds.
Although many exceptions exist, they are only there to prove the rule.