I don't think having poor damage output can be twisted into an advantage, no matter how you word it. It would be better if he had 50%+ combos consistently, instead of 17-35% combos. You could still plan your steps or setups even if he did more damage.
His poor range is a problem, yes. While I agree that it's a weakness more manageable than, say, Kirby's movement game altogether, outplaying your opponent is a poor answer. Predictability and planning ahead are player traits, not something Pichu comes equipped with. I would also say as a character he's not exactly conducive to tons of mixups, simply because his aerial game is so linear and simple (in terms of his moves' ranges, priority, etc). His ground game is overall very unimpressive too; provided you know how to deal with it. It's really easy to figure out where Pichu needs to be to hit someone, and where he's weak.
A perfect Pichu is a poor route to take this discussion because humans are imperfect. This game has oodles of room for perfection that is unattainable by humans (human reaction time and technical ability are two big factors that make such talk irrelevant). Bowser, according to some, is untouchable in perfect play because of some stupid ledgestall shenanigans he has. Should Bowser, therefore, be moved up? No, clearly not. Because that peak is impossible. It's irrelevant when discussing human play. The same applies to perfect Pichu.
I am fairly sure Unknown's Pichu is significantly better than the one in that video. Unknown almost got 1st seed in his R1 pool at APEX with Pichu (he still got 1st seed but he used Fox vs Banks' Sheik I think). Tournament wins are significantly more valuable to me than combo videos. And I'm also fairly sure the little tricks and gimmicks Unknown's told me about (and shown me) throughout the years are way more useful than the agility spam in that video...