I loved both games, they are charming in their own ways, although Skyrim sucked me in way more i still loved how Breath of the Wild managed to keep me excited for 100+hours.
For me both get 5/5
I actually think Skyrim gameplay might be better, what hold Skyrim back is the physics, bugs and writing. Since its a RPG and it focuses on writing, having bad writing and forgettable characters was one of the main flaws of Skyrim, for example the whole main quest doesnt change and doesnt have branching paths. But it has other strengths unmatched by other games.
Gameplay for example in Skyrim is far richer and allows for more possibilities, you can play the sandbox in multiple different ways than BotW. The sheer amount of skills and things to do, from crafting to enchanting and smithing, to making interesting potions to use, speechcraft and stealth, different magic spells, fun daedric items, weird A.I interactions allows for a lot of replay value.
BotW lacks enemies, items, skills and ways to play in the gigantic open world compared to Skyrim.