A) AQ5 does not have noticeable resistance. You aren't going to miss much as long as you're not being stupid / crazy bored like trying to land Thor para against Wind AQ. Honest truth #1: Either you have strong and well-invested enough grid that you can stun Andromalius within 5 turns (or 6 if you run BP), or you play turtle and tank it in the face with Jeanne + Tank SSR hime + Kaiser element cut or w/e combination that gives you 95% or more dmg cut. There is no shortcut.
B) Honest truth #2: Elemental advantage will always be superior. Huge difference in plain sight, no matter raw power, damage mitigation and debuff rate. I main Light simply because I like playing Light and decided to put all my extra resources on it. Does not mean I won't switch to elemental advantage when situation demands it. i.e. GO and Tower.
C) Honest truth #3: Tsukuyomi's debuff are nice and all but I wouldn't rely on it. In fact I wouldn't run a grid that depends entirely on debuff. Especially not with the increasing number of new contents that either counter your debuff with cleanse spam or outright no-sell. If debuff lands, nice bonus damage. I try to maximize my chance for merry big numbers too with accessories and stuff. But if it ends up missing anyway, I make sure my build can still win without it. If I lose, that means I got more work to do. Simple as that. I made that mistake with my water team and it got utterly destroyed in Fire Tower while my Light/Dark/Fire team all pulled their weight. I'm not about to repeat that same mistake again.
D) Honest truth #4: You will always assume that one will be borrowing 100%s for the hardest contents as much as possible, be it for fast clearing or simple insurance. You don't need to own one, but I see no reason why you shouldn't go ahead and borrow one for free. Other players aren't gonna restrict themselves either. I certainly ain't gonna walk into Tower without one when I have only one chance to attempt full mission clear. Plus it's ranked. You can say ranking is pointless all you want, but I want my extra medals to buy more bricks.
1. Just to be clear I don't hate Sol myself. I got no qualms about using her when situation demands it.
2. Pretty sure that's intended hinderance.
3. No and no. It's not a viable option simply because Light Team is already running short on raw stats. Vine is just a big NG. Secondly there's simply no reason to run Vine when we got Heracles who does the job better and faster.
4. Her abilities will always consume a single blade stack per use (and her burst consumes ALL). You will have to learn to time her usage of abilities in order to maximize her performance.
5. After. Another one of those intended hinderance.