The default assumption should always be that FS is active in a situation that specifically demands it and Luffy isn't emotionally compromised.
For example, if Luffy is having trouble with tagging an opponent in a prolonged exchange, we have to assume and it is the most logical assumption that FS was at play at some point (again as long as he's relatively calm).
If the goal is to grab the key from Gaban and regular CoO is clearly not working with Gaban having the clear CoO and speed advantage, it simply makes little narrative sense to assume that Luffy would refrain from using advanced precognition and simply got outsped on purpose the entire time, especially since after failing he decides to tap into awakening which means he's clearly attempting to up his speed and stats, the difference being he always has access to FS in any mode.
Once or twice is ok in my book, we don't have to assume FS was used. It really depends how dragged this game of tag is, if Luffy is using gear 2 it will all but cement to me that FS was likely used as well.
This is a fine assessment except the situation didn't specifically demand FS, the situation simply demanded more power. Whatever form that power takes is up to Luffy - he could've gone G2 for more speed, G4 for more mobility, FS for pre-cog, ACoC for more strength, in the end he chose G5.
You're talking about this making little narrative sense but firstly this is One Piece, secondly this is Oda. It made little narrative sense for Luffy not to use FS on Apoo, or when he was struggling with Yamato, or when BM was able to run up on him - the list goes on indefinitely. It made little narrative sense for Zoro to not immediately use ACoC on Lucci instead of waiting forever then bodying him in 2 seconds - none of this has to make narrative sense, this isn't HxH and Oda is certainly not Togashi.
These SHs just go with the vibe and Luffy is the chief of that. Overanalyzing why he's not using it won't get you anywhere, simply put if Oda doesn't imply he's using it then it's safe to assume he's not unless he's already 100% serious going all-out - all it takes is one small comment and in the past, Oda usually has somebody make this comment so no reason to think he'd switch up now.
I mean we could be discussing all this and it turns out Luffy does indeed make that comment and is using FS etc... My overall point is not just about FS, but that Luffy has many, many powers that he's not always using. Even if Base Luffy was using FS, he'd only be Queen level without ACoC. Overreacting to Luffy getting hype-tooled makes no sense unless Luffy is actually using a decent amount of strength, not if he's just fucking around in base using 1% of his abilities.