Note that I dont have anything against it being the best or top 5, but most people associate the top with perfection, and that would be dishonest to call BoTw perfect and sweep its problems under the rug, condemning every sequel to be inferior.
For the combat, It encourages outside of the box thinking and like previous Zeldas you have a varied toolkit to deal with enemies (previous entries had stuff like bombchus but BotW has more creative tools). But the direct swordplay has been downgraded and the slow motion dodge is basically broken, the weapon degradation is poorly implemented and the weapons themselves dont have interesting movesets (a better ball and chain than TP would have been welcome)
That's not good enough to count as good combat system. Other open world games would have been blasted for the perfect dodge mechanic in BoTW.
Then you have the divine beast/shrines being an inconsistent replacement for proper dungeons.
And the last thing is the quest design which is down right MMO tier. There's no reason an old as fuck game like Guild Wars should have better quests than BotW.
I wont fault the game too much for the story, but Its disappointing we haven't gotten a single Zelda with a better plot than Majora's Mask.