I think the main point was they were ready for a war against whitebeard pirates. However that could be true they dont want HQ to go in chaos as well.I believe it's rare too I'm with you on that, I think the sword slashes are the beginning of it. Like I think Zoro has been practicing, but hasn't mastered it ya know, like Luffy wants too, or others have shown.
I believe the awakening thing was due to plot. Not entirely plot but to fit the circumstances. As in, let's take a look at sakazuki for example, the closest thing we can conclude about awakenings for logias is changing the terrain/weather someway or another. Even if that wasn't the awakening of a logia we can still use it in this situation since akainu can do such feat but didn't at marinerford, which would've easily burned/melted just about anyone who couldn't fly.
Akainu didn't do that(and none of the other top tiers showed power like that on the marines side because) they had to protect the platform and Marine hq. They had to prevent as much damage as possible, and turning the island into a lava field would be bad lol
Edit:would've been fd up if doffy was like awakening and boom turned the platform in strings![]()
However ya like @Dino the technique used by zoro against daz bones is similar to that concept of invisible haki.