It's very cumbersome. There's a few causes for this I think.
Just looking at the D-Pad and face buttons, there are 5 buttons on this layout that do things that Zelda accomplishes with 1 button. It's called the Action button, and it performs context-appropriate actions depending on where you are, what you're doing, and what direction you've tilted the move stick. It's brilliant and allows for incredibly intuitive gameplay. Not everything needs to be as streamlined as Zelda mechanics obviously, but I think this important because the more buttons you pointlessly assign to basic functions, the less buttons you'll have to cast spells or use different weapons. This is very apparent in Witcher 3 because you can only set and use one spell at a time (which takes 2 button presses...). You have to access your quick menu to select a different spell. Gamecube Zelda games, with 4 fewer buttons than the DS4 has, were able to let players have 3x as many alternate weapons or spells actively mapped at once. Even PS2 action RPGs had a better solution to combat than this.
It's also important because the more buttons assigned to basic functions, the more burdensome movement and control is going to be outside of combat as well. Traversing the world is a bloody chore in Witcher 3, and not just because of buttons. Geralt is never as agile as you need him to be. His animations and movements feel sluggish, heavy, and imprecise. It affects combat, but more importantly it affects travel. Even basic ass stuff like walking through a door can take a couple tries, and then the camera zooms way in so you can't see what the hell you're doing. And holy shit, is that damn horse hard to get around with unless you're in a wide open field.
And then the encounter design never really gets interesting. It boils down to dodging/guarding until there's an opening, fast attack, rinse and repeat. On flat ground. For 100 hours. With a terribly shitty durability/repair system. Not even bosses encounters are interesting. This is the main thing that helps other mechanically complex games like Souls or Dragon's Dogma. There's no respite in Witcher 3. All of that, coupled with having to have a conversation with an NPC just to open up the store window, a huge "go talk to this guy in the next town, kill 10 enemies, then come back" quest system, had me quit the game before I finished it. Shame, because I loved the world and characters.