Izaw's Art of Link wouldn't be entirely applicable to this game since it was based on Smash 4 Link. You can carry some things over like how Link's Nair and Bair work or what you could and should do with Up Smash and Down Smash, but Ultimate Link and Ultimate seem like they will be different enough compared to Smash 4 Link and Smash 4 mainly in the difference in mechanics between those games.
Frame 4 jumps means everyone's aerial options are faster and more flexible. For Link who seems faster on the ground and in the air, his Nair and Bair are going to be more powerful assuming they still have similar landing lag and auto-cancel windows and they already had low landing lag in Smash 4. The fastest possible frame Bair would be out if it has the same startup would be frame 10 with a 4 frame jump. In Smash 4, it would have been out at frame 13 because of Link's 7 frame jump.
I don't play Link or know enough about him, so take this as you will. As for bombs and arrows, remote bombs are probably going to be used in a different way than his old bombs. How that affects and is applied to his game plan is left to be developed. I could guess they would be similar to how Snake uses C4, but if C4 moved and couldn't stick onto people. Or perhaps ROB's Gyro. So, more of a trap move than a throw move. Arrows I don't know. I don't know how practical it would be to shoot an arrow and try to grab it and if it can be grabbed, I wonder if it can be grabbed while it's in mid-flight. I doubt it, but if it that's the case, then arrows were slightly nerfed since people could just grab it, possibly hop and air dodge to grab it, and chuck it back at him.
What will really matter for Link, other than a universal jump frame helping him out, is his frame data. How much more damage and knockback is he doing and how that allows him to combo, follow-up, or string moves together or how well moves can kill; how much recovery does he have for his moves, were they reduced or increased on his moves; and how fast he is relative to other characters in Ultimate. For instance, if Ultimate Link is faster compared to the previous Links, but is overall about the same speed he was in those games compared to everyone else in Ultimate, then it doesn't really change much for him. He'd still be slow, but feel faster in Ultimate rather than he feels faster and is faster in Ultimate.
I don't know where that number came from unless people are not considering the fourth frame, the frame everyone is airborne when they jump or hop as of the E3 demo, to be part of the startup. That's the only thing I can think of and it doesn't make sense since it would be like not counting the first active frame of say, Fox's jab 1 which is frame 2 in every game. Fox's jab 1 is not frame 1 because it has to go through 2 frames of animation before the first active hitbox appears on the second frame. Likewise, jumps as of the E3 demo are not frame 3 because they have to go through 4 frames of animation before everyone is airborne on the fourth frame. If anything, you can't start acting until the fourth frame so saying jumps are frame 3 is incorrect.
With video quality, something recorded or watched at 30 FPS, you could just double the number and get somewhat accurate startup frames. I'm not sure how it handles odd numbers.
I'm just going to use Fox since I remember where he jumped in his introductory video. Again, use < and > to move frames and make sure the quality setting is at something with 60 FPS.
From 0:13 to 0:15. The starting frame is right after Fox has his Blaster in his holster where Fox suddenly shifts from that animation to him crouching down. From there, Fox is airborne on the fourth frame.
Edit: Oh hey, I just noticed his jab 3 is different in animation. It's an upwards swipe instead of a thrust like in the previous games. I'm watching this video of a match from Rage 2018 for those interested:
https://www.youtube.com/watch?v=thkqn2-iWZU.
