Tarmach,
I don't know Luke, and I have no details of his story other than the post you refer to, but it's unwise to draw conclusions from one example.
Airlines will always employ the best (in their opinion) of the bunch that they interview. They will interview the best (in their opinion) of the bunch that apply. They will invite to apply the best (in their opinion) of the bunch that are paper-qualified for the job. That's it. Your job is to be the best of the best (I hate that cliche!
).
There is always a danger that you can get 'typecast' in a role you don't want; instructors can get into a rut - and that comes over at interview. It was always true, and always will be. For some people, it just doesn't happen, whatever they do. This job has a lot in common with acting or music as a career; a lot of very talented people never get the break they need, or feel they deserve. The proportion of successful pilots is a lot better than successful actors or singers, though!
Don't let individual stories of woe put you off. You are responsible for your own career; only you can make yourself the pilot the airlines can't refuse.