In the end game when you get whirlwind the combat becomes a form of art. Very fluid and you start to see the designers visions.
I have over 300 hours on the witcher 3 and I found it boring at first and it got me so mad how I would die and the no auto save would make me repeat shit. but I learned and learned. Its a modern masterpiece.
Fluidity has nothing to do with it. It is mechanically shallow as a puddle. If you want to talk about fluid combat Assassin's Creed 3 has fluid combat but it lacks any depth. There aren't any deep combos and all the weapons feel very similar. Its no hack n slash and its no Souls either, just your average Western game combat that looks good but plays dull.
I'm amused to see so many people not realizing that you can't just spam a bunch of buttons and expect Geralt to do them all. Combat has animations for each swing/maneuver and each animation must be completed before you can start the next. That's why there is "lag". The combat actually requires you to use some level of timing to chain swings/dodges.
That doesn't give the combat any depth. Its pretty obvious anyways.