Yes Xyro, fair is situational, but there is a situation that is easily punishable and there is a situation that is hard to punish.
You had a fair that worked against Falcon in your 3rd match. Your spacing was such that when Falcon tried punishing with a buffered grab, he got hit. The other two or three times you used it same match, you either continued going forward with fair or your spacing was off, and you got punished.
I realize that I mistyped, I apologize, you can approach with fair, but it is much harder to space properly while continuing to advance. Additionally, if you are approaching and do space correctly so as to not get punished, it is likely you only get one flame to hit rather than two or three when forming a wall.
Now there are other situations you can use fair, but as for fastfalling or grounding a fair I highly recommend doing it only in the ways I have mentioned. Otherwise you most likely set yourself up to be grabbed. I think your way is safe to do in Samus dittos though...