Thunderspike off stage isnt very optimal at high level play and makes you lose stage control since people who understand Pikachu will always dodge it. If you do pick up this technique use it sparingly with hard reads or do it to For Glory people cuz they always fall for it.
Thunderspike is amazing offstage though!! Asides from having high base knockback, it drags people down to the bottom hitbox to make it harder to recover! I agree to use it sparingly but it can help net some very early KO's.
Thunder is hard to avoid, no matter how good you are at airdodging. Sometimes it can even catch the frame vulnerability when somebody tries to snap to ledge.
Also, Pikachu is one of the characters that can get away without stage control, since he can regain it with quick attack so easily.
But yeah, it was a little overdone in this video, not to say that this video was bad or anything.
But in competitive play, thunder would have been used a lot differently offstage.