Ok, just looked at some 3.02 frame data. 3.02 fair's super sweet spot hits for 22 damage, has 20 frames of shield damage (I don't believe this matters, but someone smart can correct me if it does for shield advantage), a hitlag multiplier of 1.4x, an sdi multiplier of 0x (idk why...), is electric type so the victim on hit (not shield) suffers 1.5x normal hitlag, 9 frames of landing lag (this could actually be wrong, I assume they didn't change landing lag).
So, if a super sweet spot fair hit a shield, here is what happens (assuming the frame after hitlag you land on the ground, so best possible frame advantage, assume in game will always be worse).
First, hitlag. The move did 22 damage, which would normally result in 10 frames of hitlag. The shielding character receives this, but Zelda has a 1.4x multiplier, so she actually receives 15. So the opponent comes out of hitlag 5 frames before us, so we are currently at -5. Next, shield stun and landing lag. Normally, this is all we have to consider for advantage on block. Because we do 22 damage, they receive 11 frames of shield stun. They have 6 frames of stun left when we go through landing lag because of hitlag. Assuming the landing lag is the same as 3.5 (you can't do landing lag in Brawl box because of FSM, so typically its done in frame advance or other methods which I don't really have time to double check), you need to go through 9 frames of lag before you can do any action. They will only be stunned for 6 of these frames, so it puts us -3 on shield in 3.02. If you have ever actually looked into safety on shield, that is pretty good. Still doesn't mean Zelda can pressure peoples shields well because high jumpsquat (-8 just to get airborne, and this is best case safety too). Also she doesn't have a shine...
For 3.5 kick, fair does 19 damage, 1.0x hitlag, 9 frames of landing lag, electric type, sdi of 1.0x (a lot of this is irrelevant...). Since we don't have to worry about hitlag, it does 10 frames of shield stun and 9 frames of lag, so at best we are +1. That is actually really good (not too many moves are positive on shield. Fox nair is +0 on shield iirc, shine is like -3 for fox, only Peach/Mewtwo are positive on shields consistently because of FC/HC). The only issue with this is it assumes you are landing the next possible frame after hit, which is even less likely for a floaty compared to say fox. Fox will be much more likely to get closer to his +0 on shield with nair (if that's right...) because his short hop only lasts 15 frames. I don't recall how long Zelda's last, but because she falls slower, if she hits the top of a shield, her advantage is significantly worse because it takes her longer to reach the ground. A middle of shield kick should be safe on shield because of the distance frame the opponent, forcing them to wavedash OoS and the lag associated with that.
Back on topic, 3.02 kicks weren't that unsafe on shield, just a loss of a couple of frames. Thats why I don't think it is relevant to make special cases when it doesn't really affect all that much. For future reference, any high damage move with low landing lag will be safe on shield (genereally, Falcon Knee, Shiek Fair, Ganondorf Fair) since usually all that is factored in is damage and landing lag. Ocassionally hitlag interferes like with 3.02 kick and 3.02 Lucas magnet (for the better), but these are the exceptions. There were a couple of things that might be incorrect because I don't know if the landing lag was the same or something similar, but all of this should be correct.