I mostly agree with you, eHalcyon, but not so much on the last three points.
5. Scout with multiple hybrid Victory cards can be worth it, but you need to have really trashed down.
6. Scout with Oasis and Inn (and Secret Chamber and Artificer etc.) is not anything like Scout with Crossroads. Crossroads actually becomes awful in a hand with no Victory cards, but these other cards are still doing fine work for you. Hand sifters and discard-for-benefit cards are definitely a combo with Scout.
7. Mystic/Scout it a legit combo. And by that I mean Mystic by itself should make you want Scout. If you haven't tried it yet, please do it before arguing this point.
5. Sure, but it's rare for the stars to align. That's what I was getting at.
6. Yeah, but that's not a point in Scout's favour. Here are the possibilities:
6a) Scout and sifter collide. Scout draws junk cards into your hand for the sifters to discard. Cool.
6b) You draw sifter before Scout. The sifter works as normal and is fine, Scout works as normal and is poor.
6c) You draw Scout before sifter. Scout works as normal and is poor. The sifter works as normal, except where it may have discarded a junk card before, now you may have to discard something not as junky. It performs just a little worse.
So it's not really a combo. Overall the result is neutral, except neutral Scout is bad. If you have the option of Oasis, it's probably better to get a second Oasis rather than a Scout to try to feed it.
7. I'm not really convinced. I can believe that it's passable. But consider:
7a) Scout and Mystic don't collide. Then Scout is just a bad card in your deck.
7b) Scout and Mystic collide. Scout enables Mystic to draw the next card... except if Scout weren't in your deck, that card would have been in your hand to begin with, and you'd have a chance with Mystic to draw something else. It's still a net loss.
7c) Scout and 2 Mystics collide. If Scout enables both Mystics to draw, you're up 1 card. Except if you didn't have Scout, you'd have the next card in hand at the start and the Mystics together guarantee that you draw another card as well, maybe even two if you guess correctly both times. You're up 1 card, which means that 2 Mystics alone are just as good even without the Scout support.
It's not until your single Scout is enabling 3 Mystics that there's actually an advantage there, and that's asking for a lot. The rest of the benefit is just in Scout's own ability to pull green cards. In a sense, Scout+Mystic kind of makes Scout more like a cantrip with the Scout effect on top, which is certainly better... but it's not much better than Vagrant.