The proper way to phrase this question is: does spending ~$80.00 in Genshin Impact, combined with the free game itself, get you an equal or better experience to purchasing Breath of the Wild + DLC packs for about $80.00?
And I say no, absolutely not. (Please note that Genshin Impact is not “done” as only three out of at least seven regions are implemented at time of writing.)
The games are superficially similar in that they share an open world with specific gimmicks (most notably updrafts) as well as fully voice-acted cutscenes, but the combat is completely different, and Genshin Impact relies heavily on RNG and grinding.
Genshin Impact is more about getting a good team with the right big numbers from “Surprise Mechanics” and grinding while Breath of the Wild has no levels, barely any stats, and responds much more intensely to player strategy. Breath of the Wild is designed to be a reasonable challenge for Link, the only playable character, and thus the challenges can be designed precisely and feature clever puzzles, some with multiple solutions. In addition, as Link does not have experience or levels other than how many hearts he is, the player is free to explore the world in mostly any order. Genshin Impact has to worry about tons of characters each with their own gimmicks; its “strategy” tends to be limited to bringing a particular element or bringing a bow user to shoot a weak point, and it has traditional Eastern RPG levels up to Lv. 99.
They’re definitely not the same experience; Genshin Impact is at its heart a gacha game. Breath of the Wild is a “real game”. You bought it for that steep Nintendo Price, you get to play it at that Nintendo Quality, no nonsense.