If you mean a more general explanation of (middle anime spoilers) how Gigalomaniacs powers work in the first place, the anime more or less hit the key points. The VN has the time and space to go into more detail of Mio's explanation but they key points were all there. Essentially, Gigalomaniacs have the ability to manifest Di-Swords. Those Di-Swords, aside from being able to be real-booted as actual weapons, basically connect elsewhere by quantum mechanics magic (The Dirac Sea that Mio talks about is an actual concept) and cause the target to perceive the delusion the Gigalomaniac has. There's some shared consciousness going on too so once that happens it "becomes" real. Taku challenges Mio on whether this is really real but as she says, if the delusion is shared by every person the question becomes moot. It's basically "the mind makes it real."
Another takeaway there is that since it relies on the shared consciousness thing, a Gigalomaniac needs another person present to make the delusions real. It's why Taku drags Gen (that homeless guy) to Serika's house to unlock the door. He needed someone else present to use his power to unlock the door.
And yeah, a lot of character background and moments are sacrificed because they don't have time. As for the one you specifically mention (Late VN/Anime spoilers) The Senri stuff comes off as incomplete, IMO, because that's the Kurusu Route stuff I mentioned. In the Normal Route it never goes into that. The hints are all still dropped, like Arimura picking up that she lied about seeing Senri crushed (though this is handled a bit differently and becomes part of the investigation around the time of the pyrokinetic.) Along with additional ones like what the deal was with Senri's ID Card. But it isn't unless you go on Kurusu's Route that the reveal that Kurusu is actually Senri happens. The anime instead takes that part of the Kurusu Route (but almost none of the rest of it) and tries to cram it into the Normal Route which makes it comes off as awkward and Senri ends up disappearing because none of that happened in the Normal Route so it presses on and there's no real way to fit her in there. In her actual route in the VN she most certainly does not disappear and things go very differently. Taku arrives at the duel between Serika and Senri before Serika can win and Serika flees before Senri even drops her disguise for instance! ---
xp1337: Don't you wish there was a spell-checker that told you when you a word out?