I think the juxtaposition can go even deeper with Shamrock having been robbed of his freedom while having the highest position vs Shanks who lives in the lower world but kept his freedom.
I like this a lot.
Oda has shown us that, outside of Imu, the Celestial Dragons really are the biggest slaves in the series. They don't even control their own emotions.
And Imu themselves seems to be a slave to their Demonic powers/Lili/Nika/the past in general.
I think that's why Shanks/Roger/Luffy types just piss the CDs off so much. It's the same thing with rich people when they see like, an interracial lesbian couple be happy.
When you've spent so much time selling this lie that you are superior, and the people you dislike are beneath you and miserable, and then you actually realize that, with all your wealth and power, you're the miserable, lonely freak, and the "plebians" you've spent so much time attacking/judging are happier than you are?
That has to be the most miserable feeling. Like, look at Shuri compared to Gunko.
Shamrock seems to be very intelligent. I think Shamrock realized a long time ago why Shanks chose the lower world over Marijoa: it's because it's real. The Holy Land is just a grand orchestra of lies and bullshit.
Shanks' smile is real, when all we've seen from Shamrock is a cold grin, at best. I think Shamrock craves humanity, craves the freedom Luffy represents.
Shamrock was introduced with Gunko, who stated she feared Nika most. I think Shamrock is the opposite, and wishes for Nika to free him.