I believe that because Dragite negates activations, it actually could use the negate even in the damage step. But you're right that Gigantic can just attack over it first!
The great mistake in the first match was not put gryphon under elf to gain the protection. Another mistake was not negate the genroku with red. Tenpai dragon red can only be special summoned only if another fire dragon is on the field.
Can't activate its effect once the Battle Phase Floodgate comes out. That's usually late into the combo but sometimes they have everything they need to set it up early and then you're screwed.
All spright versions are still good. The difference is in the numbers of extenders( dead cards if you draw them) that each deck uses. For example this version in the video uses 8-9. The fiend version uses 1-4( hero kid with any spright or gates isn't dead but without them it is). Live twin was around 4-5 if I remember correctly. Otherwise all spright versions can play around 1-2 interruptions and end on a 5-6 interruptions board easily
It's probably one of the better versions since you can just pop the field spell as they set it up with Li-La, even better if you can double that up with Carrot/Smashers. Just have to watch out for Board Breakers since Tenpai plays a ton of those and you're usually only able to negate one at a time unless you do some crazy stuff with Delta and the Psy-Frame Link-2.