I think you need to reframe the scope of your post a bit.
All airlines I am aware of support letting Canadian PRs without an eTA board flights to Canada. I have yet to hear a report of somebody being denied boarding.
However, many airlines (including the ones you mention above) may not have bothered to properly configure their self-serve check-in tools (web / mobile / kiosk) to handle these situations. And if, like LX, I have one flight a day to Canada, I will probably not make this a priority for my dev team either.