It's not especially.
It "feels" that way because now you have to chose between moving and auto attacking. There's more strategy in positioning and timing of attacks.
Then, you need to charge arts with auto attacks whichare not available at the beginning of battle, also making it look like slower.
Not to mention they almost only play with Rex which is equiped with 3 slow weapons.
Watch Nia, she's much faster.
The last points can change depending on your skills/arts (most likely), character, weapon and so on.
I'm sure it will feel good when actually playing it. Can't wait.