It is the way you're playing. Don't take offense, because that's a good thing, since it means better experiences are possible.
Honestly, sometimes if I play this game too much, sometimes I find myself on a shitty run of form, and it's all me. And now that I've moved up to Legendary, any drop in form on my part means conceding goals - sometimes lots - to the CPU.
Regarding a lack of movement when attacking, I do know what you mean. I ran into this problem yesterday. I'm not positive but I think it boils down to playing the game too impatiently, and often times relying on sprint more than I should.
I'm not 100% sure what's going on when I'm playing like crap, but I think these are the keys to my game when I'm kicking ass:
In attack, when I'm playing my best I'm not prioritizing trying to score, rather I'm focusing on retaining possession and moving the ball around the pitch. I find that when you shift your focus from trying to put the ball in the back of the net asap to simply holding onto possession, things open up and some really nice football is possible.
Similarly, in defense I find that I concede rarely when I'm not prioritizing getting the ball back asap but rather focusing on retaining my shape and then closing down the space. Play the space, not the ball, and whatever you do, do not let defenders (especially your CBs!) get pulled out of position. When it comes to defending, less is often more in this game. Play too aggressively and you'll get burned, especially on WC and Legendary, and even more especially on default settings.
Maybe other people are different but those for me I think make the biggest difference in my success and enjoyment.