Just to clarify, the "sequence" mode on the Siglent is not about some difference between waveforms-per-second stored in memory vs displayed on the screen (as might be suggested by the message at 7:26), nor is it useless because it doesn't improve detection rates of runt pulses, nor is it even designed for that purpose.
It should probably have been named "sprint" or "burst" mode to hint at its usefulness. Contrived example, if you have a MCU that blurts out 1000 SPI packets separated by 3us each, and you want to capture every single packet in segmented memory mode, you need a scope that can retrigger on 3us intervals. And since a typical scope has no sort of "sprint" or "burst" capability, that would imply a requirement for 333k waveforms per second -- so, forget about any Rigol on the market, even the DS6000 series. Any scope that can't capture 333k waveforms per second, or (less deceivingly) waveforms on a 3us spacing, will miss packets. But Siglent's scope, in sequence mode configured to 1000 packets, will catch every single packet and allow the entire transaction to be replayed.
In short, it's about capturing 400 waveforms in a single millisecond, which very few scopes can do. The 400,000 waveforms per second does not mean that the Siglent can capture 400,000 waveforms in a single second, it clearly cannot. Just like a human can run 100m in 10s but that doesn't imply a human can run 100km in 10,000s. I think that feature has been misunderstood, even mocked a little in these videos, especially with the "woah, look at that huuuge blind time" commentary. Nothing's happening during the blind time in the intended use case for this feature!!!