This is going to be fairly hard to accurately comment on, without knowing which videos, and times that these images are taken from. I'll do what I can.
I presume that the video is supposed to show that the small time taking this step leads to a superior action. Ether the step will allow you to hit, or it will enable a second intention. But I just don't see that. In fact, on closer analysis I think the video shows the opposite to be true. I think it highlights why the time spent stepping left and then passing across an initial fendenti is not good.
Lower arrow highlights how the attacker has exposed his outside to the defender. This allows the defender to more easily gain the attackers back via playing on the left side or yielding under the cross. Also note the twisted torso which will aid unbalancing of the attacker should the defender get to the outside. This also means if the defender "goes left' the attacker will have to twist around even more to follow them. The upper arrow shows the exposed right, forward forearm. Very vulnerable to both sniping and second intention.
His feet are wrong for longa, and if this is the end result for a demo of the footwork Richard and I advocate for attacking from di dona, he's attacked entirely too soon.
Your assertion that the defender can gain the attackers back is certainly true. It's also true that the defender may not have the tempo to do that, since he could very well be staring at that point. It is also possible that the defender eats that point. Either of these things are possible, since the defender's tempo and measure are not shown.
As to the right side being open, you're quite right. However a straight on attack, as you advocate, would leave both the left and right sides open to attack. So, the footwork, even being incorrect for longa, has closed off a line of attack. You also ignore where the back foot is, it's still able to keep the point online if the defender actually has a full tempo to act, and even increase the measure if necessary.
Since we're not discussing whether di dona is right or wrong, I'll leave the "this isn't di dona" red herring alone, and snipped for brevity
Defender steps in and gets hit. However, note the posture of the defender. He has leaned back and crumpled his arms under his counter attack. He finds himself on the wrong side of the attackers sword trying to power though the attacker with no structure behind the cut where as the attacker has both superior structure in his cut and I believe superior physical strength. In the video if you rewind a few frames, you will see the defender fold in on contact to this crumpled position. You may argue that this is due to a superior angle of attack, however note the arrow by the foot. Had the defender maintained structure with good arms and posture, he would find himself on the outside of the attacker and in complete control via simple yield.
This happens a lot when you step sword side slightly, and pass at an angle. You cut at your opponents sword side, not their off side. The footwork, plus the targeting reduce your opponents reaction tempo and measure. You force the defender to either move fast enough to intercept the attackers blade early enough to throw it over the defenders head, or you miss the defense entirely.
Without knowing which video, and time this happened at, I can only speculate that this is what happened.
Just parry. Looks like a good parry and it looks like the defender here is in a good position to repost as the defender has control of the centre and the attacker is twisted up, sword to their right, and body angled left. Since this is kinda like Fiore's go-to defence, this is the expected result. Attackers hands are high, I suggest ruining down the sword and ruining the hands followed with a thrust to the face.
Yep, Richard has clearly has this one. Again, a video and time would be nice to know if this is the result of the footwork or not. It is interesting to note that had Richard's opponent better footwork he'd be in a better position (still in boat loads o' trouble) to counter what's hopefully coming next. Center weighted like that he has to unweight himself first, allowing Richard more time to work evil on his opponent.
Both do the same thing. Defender here has won, completely. He has the back and the attacker is completely twisted around trying to follow the defenders movement to the left.
I'm assuming you mean both attacked di dona? If so Kyle has clearly passed to deep, probably helped by richard countering that nicely.
Stepping slighltly off the line and passing at an angle can be tricky to do, and when both do it, you end up in weird places. The one who predicts their opponents movement best wins. This isn't really any different from any other footwork.
Defenders charges in. Note the defender yielding under the blade and taking the attackers back. The video shows a FUT resulting, but with reasonable execution this is easily one of a numbers of Fiore's stretto plays. I see an obvious pommel strike coming myself.
If this is after the previous, I think it shows what happens when you end up balanced. Your feet forget to move, and Kyle has clearly stopped moving his feet. Richard however is continuing to move.