>>23387919No moron, it does not lose its flying typing on the second turn. The pokemon becomes grounded. Grounded is a condition where a flying type or levitator loses its ground immunity, but retains both its actual flying typing and all other related type match ups. We've seen this with iron ball, we've seen this with smack down, we've seen this with gravity.
You say types have inherent effects that aren't just bypassed, but that's literally what happens in all the examples listed above, and it's also what we see on the second turn of thousand arrows. The ONLY difference, the only caveat, is that the first turn of thousand arrows all flying types are hit for totally neutral damage regardless of secondary typing, ruling out possibilities of a hidden ground resist under the immunity. Which is why thousand arrows is perplexing because it's an inconsistency that happens nowhere else.
