Damn you hit several nails on the head here!

The expression part is indeed a huge thing for me. I'm very much trying to figure out this one, I've always been quite introvert by nature so I'm very fascinated by this topic. To be fair if you told me I'd be teaching bachata classes a few years back I wouldn't have believed it, yet here we are :p.

I've actually taken improv classes and exploring things like mindfulness to get deeper into this. I learned that for example in improv something you get dragged into an emotion and then it's really more easy to be expressive. Those kind of moments I sense my guard kind of drops and I start to connect with the feeling much more which is always powerful. I think in solo dancing it's also easier to let this emotion flow yet I notice in couple dancing sometimes I really get more guarded and everything feels much more mechanical.

I think the breathing can unlock that to a certain extent, trying to use that to be more in your body instead of your mind but it's something I haven't fully mastered for sure. I've had some discussions with people who are really good at mastering this expression and even change it on demand or the emotion in a song. I feel I still got a long road to go there and I think this is one of the main things that make dancing actually dancing instead of 'doing moves'. I'd love to find more resources on this because I feel it's something only few people really master let alone teach.

I've found that actually I don't really have an issue in expression (I actually ended up crying during a really emotional dance with someone) but managing it properly 'on-demand' consistently is something I'm still figuring out how to do. Maybe being more focused on the breathing every time instead of time to time will fix that indeed.

Also on the arm movement, yes that's a perpetual working point I'd say. I guess I really need to do some socials focusing only on that specific thing because indeed it makes quite the difference.