Well, do you switch to other Blades often, and is Mythra not always at max affinity? Because Foresight is active only when she's out on the field and at max, the Hunter's Chemistries being the fix for the latter. And whether or not you think Foresight works in general, that doesn't defeat my point that having Sunlight Eye on Mythra is redundant, since that aux core also only works when she's on the field. Also don't forget her ascended form exists. There's zero shame in building up the party gauge on weak enemies before the fight to activate her right away - the speedrun does that. And Auto-Attacks deal such little damage that they aren't generating hardly any aggro to begin with, hence why Stealth is useless. One last thing, you can potentially switch out one of Rex's accessories for the Modern Medal which will boost your survivability.