When looking at Nintendo's output during the Wii U days, I feel that the vast majority of their titles, aesthetically speaking felt, lighter and softer than normal, even by their standards. Nintendo has always been known to be family friendly and non-conformist, and I love that about them, but with the Wii U, I feel that was taken a bit too far with their games. Like Super Mario 3D Land felt much more colorful and less epic than the Galaxy games. Star Fox Zero felt like a massive step backwards in terms of story and tone. Nintendo Land felt more colorful and saturated compared to Wii Sports, Smash 4 felt brighter and more whimsical etc. There are the rare exceptions with Nintendo publishing Bayo 2, and the Wonderful 101, but you also got controversies like the Xenoblade Chronicles X and TMS censorship debacle.
Comparatively, Switch era Nintendo games feel much more balanced. BotW is ambient, mature, and quiet. ARMS is cool, flashy and epic, Splatoon 2 feels a lot more anti-establishment and in-your-face than the original game. Super Mario Odyssey brings the grand epic-ness from the Galaxy games back, even throwing in some darkness for good measure. 1-2 Switch and Nintendo Labo feel quirkier and more stylized than the somewhat sterile aesthetic of Nintendo Land, Ultimate returns to the more serious tone and feel of Melee and Brawl.
Basically, Switch era Nintendo games feel much closer to what the Nintendo style would actually be like with modern hardware, whereas the Wii U era felt more like a cheap imitation of Nintendo's aesthetic. This goes for marketing as well. Wii U tired too hard to pander to young kids, but Switch is a cool and sleek device that can appeal to the whole family, as well as other audiences.