The only part I disagree with is his comments about MotoGP. Those guys don’t do delayed apexes unless it’s a decreasing radius corner, etc.
On the track, there is generally a racing "line" that is the fastest way around the track. There are defensive lines, and then there are the fast lines. Defensive lines will often preclude delayed apexing because doing so gives your opponent room to slide up the inside and do a block pass. The defensive line is typically not the fastest way around the track for either rider, but it hopefully keeps the chasing rider behind the leading rider.
That said, sometimes a delayed apex can be used to pass a defending rider. Dovi has used this on Marquez on the final corner of several races to great effect! Marquez made last ditch effort dives up the inside but carried to much speed, making him go deep and wide. Dovi stayed to the outside and then cut back under Marquez as he went wide, taking the win because he was able to carry more speed through the corners.
If you watch a rider that has pulled clear of the bikes following him, he will start using delayed apexes to carry more speed through the corners. However, he still has to stay on the basic racing line, which is not truly a line but more of a path with some width to it. That path is usually clean pavement. Get to wide outside that path and you start getting into bits of rubber, dirt, dust, etc... This can easily cause a rider to crash or to at least have to slow dramatically to keep from crashing. So they delay apex within the width of the racing path, kind of like a street rider staying in the width of their lane.
On the track, visibility all the way through the corner isn't always an issue like it may be on the street. A big reason for delayed apexing on the street is to have more time to better see through the corner in case there is something you need to react to.
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