Have you seen how imbalanced the character stats are in Mario Kart 8 Deluxe? Metal Mario and Pink Gold Peach have a higher stat total than everyone else in the game, while the characters with the lowest stat totals are "all" lightweights.
Mario Kart 8 made sure that everyone shared the exact same stat total (excluding the mini-turbo stat, which decreased as the weight stat increased). And I can confirm that heavyweights don't always get their own way in that game, as I have lost to some very good lightweight and middleweight players throughout my online racing career, even when I used a heavyweight character. In fact, it's the lightest characters in the game who can achieve the best possible stat totals with their vehicle combinations, since the heavier characters have weaker mini-turbo stats.
In Mario Kart 8 Deluxe, however, it's pretty much a Metal Mario and Pink Gold Peach show, as no one else has the stat totals to compete with them.
Still, the focus should be to improve the low-ranked fighters first, because you're not exactly helping them with their problems if you're only nerfing the higher-ranked fighters.
Once the lower-ranked fighters have been improved, "then" the focus can turn to nerfing the higher-ranked fighters.