You did say "I'll add that flat trajectory is always nice to have, but can you get your fixed blade broadhead to fly accurately in high winds on those long shots, with a light arrow? Probably not..." which sounds like it can't be done.
You shouldn't read the words "probably not" as "can't". They don't mean that. They mean that it's not likely.
It can and has, but like you said later, it may require more time to tune. But as I also said, a long shot in high winds should not be taken with any setup. Too many variables.
Pick a distance, any distance. Add wind. Which arrow is more stable in that wind?
If most light arrow combos that you are referring to are with tips lighter than 100 grains, yes. A 100 grain tip will give good FOC and a 125 tip will almost make the FOC too high.
Too high an FOC with a measly 125 grain tip? Not likely. Too high an FOC only affects trajectory. It makes for a very stable arrow. Even if it's a youngster shooting 35 lbs and a super light arrow, they'll have to limit shots to very short range, and the extra momentum from the heavier tip will be much desired.
Look, all I'm trying to say, is that decisions geared towards faster flight typically make an arrow less forgiving. The only advantage for speed is distance estimation, and that is not something that should come into play on most hunting shots. First of all, they're typically very close, and second, we have lots of ways of getting the distance exact before the shot, ie.. pre-measure, range finders and practice.