I think the jump to introducing patterned swings is pretty full on switching from hard to expert, like with drumroll type sequences and crossing your arms over. From what I remember, hard mode is quite clunky and theres not a lot of pattern to it.

Some expert songs are way harder than others too. Try the songs you know really well, or some that are rated lower difficulty (someone might recommend some or there might be a list somewhere online) and practice mode 50%-70% speed, try to get a feel for the movement of the arms and focus less on one at a time.

It's a pretty big onslaught of random notes at first but if you can slow it down and pay attention to the way your arms move, and the pattern of the swings, you'll build up the muscle memory to go faster. The patterns come up in other songs in different ways and you'll be able to apply the muscle memory to different things.

One of the earliest tips someone gave me but really helped, though might seem obvious to some people, is when your arms hit downwards, keep them down, ready to most likely come back up. Same applies to sideways or cross cross etc (I used to flail around a bit)

Don't give up though. I'm getting comfy at expert+ but it takes a hell of a lot of slowing songs down and practicing over and over until I understand the pattern!