No-one is underestimating his skill, Boruto is just ******* stupid at making sense scaling wise, they were literally Chuunin level in skill, even beyond that, as ******* Academy Students. Also why would he, esp his part 1 version, go all out and for the kill on Sarada who is a literal child, esp given the fact that she's a literal leaf ninja. Also, Sarada would go into the fight fully aware of who Kakashi is and what he's capable off, so she literally starts with an advantage in knowledge.