I think there was too much going on in KH3 that they didn't really do the interactions that great or they didn't have time for it, but there were also moments that weren't exactly necessary, which they could've omitted, such as the part when Riku, in half-awe, asks Sora how [he got to the RoD]. Sora will have explained that to the others later offscreen anyway, and it's awkward for Riku (him being a Keyblade Master and all) to be asking that in the current situation, completely off-guard, when his friend Mickey is injured and Anti-Aqua could strike at any moment (literally she's just standing on the water idly; that's something that KH3 did a lot, leaving characters standing there doing nothing/eerily staring at the present interaction, which wasn't good because it made everything seem slow and unrealistic, and honestly made me cringe at times). If they had omitted such parts, they might have been able to add something with Sora worrying about Aqua.
There definitely is a lack of Sora caring about Aqua, which I don't necessarily like either. The times when he burst out that he wanted to save Aqua and go to the RoD was because of Ven's will, so that doesn't count for Sora himself. Yes, there is the fact that he doesn't know her at all; he's only heard of her from Mickey's letter, and he doesn't remember meeting her when he was a little kid at Destiny Islands. If that was it, then I'd understand why he didn't really express any concern; but it isn't. In Blank Points, Sora is determined to save Terra, Aqua, and Ventus, as he says, "I am who I am...because of them." In that scene, Sora's clearly concerned about them. But in KH3...well, like you said, he's just neutral until he saves Aqua. And even with Terra, he doesn't express much.
This isn't the only part where there's a lack of concern between characters. When Kairi is kidnapped and struck by Xehanort, Axel....appears to not care, which is strange, considering how we see the two bond in the Secret Forest while training. Like, why show them form a friendship if Axel is not going to care about his friend in the end?
I think the main reason why these things didn't happen, though, is because there was already enough content in this game, which is why I'm not going to whine about it. Sure, it would've been nice to see those kinds of interactions, but the team had been working on this game for so long, and this game had far more good stuff than bad, so I can't really complain.