The best year is already behinde it.
2017 had Zelda BoTW + Mario Odyssey + Mario Kart 8 delux + Xenoblade Chronicles 2.
No following year(s) is going to beat that for the Switch.
Those are the biggest heavy hitters Nintendo has, and Switch got them early.
Switch 2020 is like Animal Crossing + Xenoblade 1 + Tokyo Mirage Sessons FE.... not a big year.
If you think thats all the Switch is getting in 2020... think again. We still don't know half the story.
Even if Metroid Prime 4 + BoTW 2 also launched in 2020, it still wouldnt beat 2017 lineup.
Also I doubt Nintendo does that, they want to save some to spread out for 2021-2022 as well.