Idk those hills beside that PW crater don't look that large to me. I'm pretty sure Onigashima is tiny too. I'm not convinced that hole is bigger. Didn't we see Big Mom falling into it, wasn't
that large. Could be wrong though.
This looks like a joke
Those hills are at least larger than the hills on top of the skull. There was a door to one of these hills, like 1/4 of the hill's size, where Numbers could easily fit in. Yet, these hills are drawn quite small very often.
That's the thing, Oda isn't drawing this detailling when it comes to landscapes, mountains, etc but he's cleary making sure this world is as big and ridiculous as it is possible, where you can randomly see a mountain sized sword next to the skull or gigantified places.
Furthermore, if you look at this panel, it's insane how deep the hole is:
The hole is even double the size of the ocean's depth in this panel. Law always delivers, lol. But it put in perspective how crazy this feat would look like if Kishimoto drew this.
As for Big Mom being visible, I don't see this much of an issue considering Oda often draws characters very visible to big objects, so that the reader knows their position (that's what I'm assuming)? You can see the same thing to Luffy being near the noah and Zoro being visible in front of Pica's golem, even though it carries multiple multi story buildings and its arm was described as an entire town by Usopp.
Are you under the impression that Imu is familiar with all those guys? At the very least, he couldn't have been 100 percent sure about what powers Kaido has, and I doubt he knows much about any of the others tbh. This is literally how all HK, Gorosei etc act, they like showing off their Regen, and Imu has an even bigger god complex about it. Itachi is simply a terrible matchup for characters like that, you would need someone like Shanks or Kata to fight him, but putting them against the entire Akatsuki is just absurd.
I think a dragon would be more ordinary in Imu's eyes than a gigantic spiritual menacing looking warrior with a sword.
Yes, the chance is high Itachi just hits Imu and absorbs him but like I said, the vessel gets absorbed and then? Imu knows what Itachi can do and is more prepared this time... till he gets put in a genjutsu, lol. Yeah, Itachi is quite broken when characters are in-character. Honestly, he'd own many arrogant DBZ or Bleach characters as well, since his illusions are pretty broken and can nearly warp the reality within the illusion. If Aizen's illusions were fooling everyone, imagine Itachi's...