My heart never beats so hard during draft as when I have 1 life left and I swing out for barely lethal with double trumpet blast for 15 unblocked damage. "Please don't have removal, for the love of god"
I do the same, GB. I can't draft anything but UR tempo; sometimes splash white to be Jeskai, and sometimes green to be Temur (with a preference for Jeskai). I agree with most of your points, although I'm not super impressed with Mystic of the Hidden Way (it's not super mana efficient, and the archetype is all about subverting the expectation that you have to invest oodles of mana to have meaningful board impact).
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Mystic is the best possible ground creature for Jeskai. It's free repeatable damage. It's also your most mana efficient morph, since it unmorphs for three. That means on turn 5 you can either drop a mystic or morph it + a 2 drop, then unmorph next turn and attack with a 3-mana spell up like trumpet blast. It comes down around the time your opponent stabilizes and if they don't have removal the game is over. It's also a 5-drop, not a 6-drop like the other good morphs which is important. It's your most evasive creature, and it's a pretty good clock.
Don't think of Mystic as a creature you have to spend more than 3 mana on. Think of it as a creature that has a spell attached, you don't need crippling chills and force aways to guarantee damage with it. I can't overstate how crucial the card is. Not having at least two is brutal.
As far as splashing, I'm doing it less and less. If it's something like Mantis Rider or High Sentinels, than yeah. But I'm passing pretty much everything that isn't UR. I don't even play Efreet Weaponmaster or Warden of the Eye anymore. I don't ever want to stumble on mana. I even passed two Elephant Tuskers when I built this deck.
That said, I've been leaning towards Temur more than Jeskai lately just because of how insane Savage Punch is with Bloodfire Expert.
I would also put Treasure Cruise high on the list. You're constantly casting spells which go to your yard, and your opponent is trying to remove your stuff; I cast that card for 1-2 regularly in this archetype.
I mean, it's fine. It doesn't do anything that you really need if you're playing crippling chills and weave fates. Sorcery speed is something that's really annoying to me, which is one of the reasons Mardu Warshrieker is going lower and lower on my pick order. I want to play things during combat or my opponent's turn.