I can't speak for anyone but myself when answering those questions.
However, I would say that the biggest case for having lightweight is that her default down b, counter, is not only a move she shares with many other characters, but she also has objectively the worst one, both in hitbox size, knockback and frame data.
I will be very happy if that move alone were to be replaced with Lightweight. Counter is awful. I would go as far as saying that if you were only to have 3 sets, counter shouldn't be in any of them.
I'd say her up-bs warp and jumpglide are both very viable moves and I don't think it matters as dramatically. Same with her first two neutrals. For that reason, I wouldn't care if either are used. Jumpglide has been popular as a combo extender and because it allows you to hover at a good height for spacing a fair. Explosive flame has been used more too.
In answer to your question, lightweight changes everything and is incredibly important.
I'd rank super speed below that, but still very important. It's an interesting move, but fairly balanced as Palutena is vulnerable, it's unspamable and if the opponent DIs correctly after being hit to avoid follow ups, it only does 0.5% damage. This move changes Palutena massively, as it gives her an effective and safe on shield rushdown mixup.
The other moves are personal preference. I personally would be fine if they remained default. When I play her, I use autoreticle and warp anyway.
To make this more on topic, I think M2K not being at EVO was potentially disasterous for Palutena, as he was going to play her. Aerolink also placed 9th with her, which I'm very happy with, but I haven't been able to see any vods of him there.