A little thing I enjoy is that Dongfang Qingcang is smaller than most of the rest of the men in the cast. Not only is he shorter, but he's also not as broad. By no means is Dylan short (he's decently tall), but he's just not as big a dude.
Cangyan Sea Boy Band pic, and everyone in the image is notably quite a bit larger than him with one exception.
ZLH is of course several inches taller than him, and he's broader too. DFQC is given a lot of clothes by the costume designers that make him look bigger. Notice the second robe in the first pic, whereas Xiao Run is only in one layer.
Comparison when they're both holding Xiao Lanhua just to show HOW MUCH bigger Changheng is.
And with Shangque! He's not wearing a second robe in this shot, so you really got an idea of his actual frame size.
The one character he seems to be very close to size in is his brother, which makes sense!
I don't think they deliberately cast these actors based on my observations per se, but the idea of DFQC not being a big man, but being the most powerful in the three realms appeals to me. And it also appeals to me because he wears SO MUCH clothing, and it tickles my blorbo rotating brain to imagine him doing this partially because he knows he's not large, and he wants to be visually intimidating.
I especially think of that massive armor. He doesn't just wear it on the battlefield. He wears it in meetings with advisors and with the two kings. There is no reason for him to wear it there except presence. Yes, it could be ceremonial, but he's also in the throne room without it from time to time.
Even on the battlefield, no one else in the series has armor that huge, that cumbersome. I'm ignoring the impracticality of it because none of the armor in this show is practical, but I really like the idea that he chooses that armor not only because it's intimidating, but because it makes his (not very imposing on its own) figure look much bigger than it is.
Also remember that Dongfang Qingcang became Moon Supreme as the equivalent of an ELEVEN YEAR OLD? He no doubt had to make himself look stronger than he physically appeared at first.
