As Pichu is a kid, and Gv kinda lacks experience fighting those (I mean, the closest he has fought in around those ages is Zonda), which means that GV lacks experience fighting minors, which means that Pichu can be a bit unpredictable to GV, especially considering he won´t be especting much more than a few sparks from Pichu at the start from the fight, which means that Pichu can use Encore and Endeavor in a proper way.
Lastly, for the electricity absorbing thing, I´m sure it wasn´t game mechanics, as Asimov even said that he had the same septima as GV, meanig that they were comparable, which means that GV can´t just absorb electricity proyected in a way similar to the flashfield (as I know someone can bring up about Copen´s Steel Spark, which GV can easily absorb, but unlike Asimov´s flashfield, that move is proyected directly by beams of eletricity, not as an omnidirectional AoE, which means that GV can´t do much if Pichu uses Discharge, which is pretty similar to how the flashfield works.
I´m also sure Gv can´t dodge Disarming Voice except by Prevasion, but to keep it with it, he would have to literally stand on the same place for a while to continue recharging, something Pichu can take advantage of to get close to him with a Volt Tackle and then just use Discharge.