Have you checked the smoke point of flax oil lately?
I use refined "extra light" olive oil as my neutral cooking oil, and that's what I use to season with (though I'll use EVOO sometimes if that's what's nearby). The smoke point of extra light olive oil is around 470F.
I don't think that an oil's smoke point is a reliable indicator of its ability to season pans (provided that you're not using something like avocado oil that has a smoke point higher than your oven might go).