Some random thoughts on how the shine on every char is ultra busted:
I'm gonna start with Luigi because this one is ridiculous and I don't know how someone got to the conclusion that this is amazing. At all. Fox's shine is not broken on Luigi because Luigi still has to get close to the opponent to set it up. He has no dash dance to do this, a slow walk, no good aerial approach, etc. His only way to do this is with WD and most characters focus on shutting his WD down. Can shine interact with Falco, Fox, Falcon, or Sheik platform camp? No. Can it interact well with dash dance grab > lol combo? No, not really. Can it interact well with needles, SH back, lasers, and other lame Falco & Sheik things? Not much more effectively than his current tools. If you want Luigi to succeed, he needs a move that extends beyond his current range really effectively and offers a challenge to these characters' control mechanisms from a distance. This is similar to why shine on Marth isn't really broken, just an upgrade from counter but we'll talk about that below.
Marth doesn't have the close-range aerials to make shine an effective pressure tool. Similarly, his game largely revolves around keeping distance - the shine only functions at close range. Now, whether giving him a reversal that's actually good is worth consideration. However, shine > WD > tipper f-smash is not broken (given how limited his setups are for it) and the amount of influence DI can have on the success of that combo is huge. Being able to shine spike and Up+B recover on low opponents is cute, but not that functionally different than his numerous offstage things that currently exist. I guess it helps gimping Peach though.
Ness still has bad range and no lead in for it because he has no threatening aerial. His uair chain still sucks and he can't reach anyone after like 50% aside from the FFers. In order to buff Ness, you want to make his SH and FJ accel speed higher so he can reach people during the DJC chain better. You then just want to give him tools to access his DJC chain (and probably improve the chain itself). He's not fast enough to use the shine after leading in with an aerial and his conversions off them are weak (bad ground game to follow Fox's, bad DJ for following Falco's).
Actually, I'd like to address the DJCers as a whole here. People are intrigued by a shining Yoshi or Mewtwo. I'm here to tell you, they're not that interesting. The DJC characters collectively need different things because they're not built like the spacies. Mewtwo's air mobility & floatiness is actually really powerful but he lacks the aerials to make it work. However, if you gave Mewtwo a good fair (think Sheik-esque hitboxes but with his hit properties) and an improved f-tilt or u-tilt to hit above & in front of him (to police people who beat him by aiming at that blindspot) and an improved side-B (set stun, not immediately prone to counterattack) he becomes a phenomenal character for a whole variety of reasons. Yoshi benefits from a proper grab & jump OOS way more than he does from shine. Shine doesn't address many weaknesses.
I'm also gonna address Puff. Shine on Puff (assuming she keeps rest - let's say she loses sing) is not as great as it sounds because she lacks the speed to follow up on it effectively. Her jump is tiny. Can you imagine her trying to chase someone after shining them with Falco's shine? Her aerials are also medium speed for the most part, so she doesn't have anything like Falco shine-bair or shine-dair to force automatic combos before they fly away. She doesn't struggle with low height offstage gimps currently - she's already great at edgeguarding those. If you want Puff to be broken, give her a throw that sets up rest, a simple tech chase, or an air combo on floaty / mid-weight characters (Sheik's d-throw, for instance). This is way more brutal than shine - all of a sudden, being grabbed by Puff is a thousand times more dangerous. Or, if you really want to play to the theme of Puff as a scary character, give her one of the existing air grabs. All of a sudden it's unclear whether you can shield her when she's jumping. Think about how drastic a change that is for almost any character that fights her. Puff with Inhale is ridiculous IMO.
tl;dr it's a great counterattack and shield option. It can stop you from being projectile camped to some degree, and it can set up useful moves. That said, not everyone has these useful ground moves, the physics to follow the launching shine, or the aerial game to lead into it. A lot of characters benefit way more from fixing their existing problems - this may include an OOS game, but often there are more pressing ones.
