The way to evaluate the contradictory claims is to find a source who did careful, controlled-variable testing of flaxseed oil vs. other oils for seasoning cast iron. Neither of the sources cited in those questions is such a source; one is a chemist who arrived at flaxseed based on chemical knowledge but didn't compare with anything else, and one is a publication that rejected flaxseed oil based on reported problems, but didn't share their methods or apparently do direct comparison testing.
My personal experience with rescuing a couple cast iron skillets was that flaxseed works quite well, producing a hard, nonstick surface. I also use the heat-and-wipe method rather than the invert-in-the-oven method. But ... I didn't try to compare it with anything else.
So, did anyone?
The Kitchn & Cook's Illustrated tested and liked Flaxseed oil, but didn't test it head-to-head with any other oils. In fact, the Kitchn says:
There is one school of thought out there that says it’s not the flaxseed oil but the method that makes this work. In other words, season a cast iron pan six times for 18 hours with any oil and you’ll get a hard, slick surface.
Also, note the number of preconditions and steps in their method; certainly failures with flaxseed could certainly be a result of violating one or more of those "rules".
While one can find any number of comparisons of oil for seasoning, you'll find that none of them do any scientific testing. Grapeseed oil is also popular, as is refined coconut oil. The usual sources of science-based data for cookware are mute on this topic because cast iron is rarely used in professional kitchens and never in industrial-scale food prep.
So if you want The Answer on which is the best ... you're going to have to arrange testing yourself.