Tracking Invulnerability:
In tandum with the previous thing, if a bunch of players show their view as hitting a specific target, and that target takes no damage, then it's an obvious invulnerability hack.
Such as this one time I came across a Caustic. I pumped 4 Eva 8 shots into him as he turned towards me and 2 more as he fired upon me. Every shot had at least 2 pellets hit, most having 6+ hit. He opened fire upon me with a Havoc and wiped my 200 HP (purple armor) in 0.2 seconds. He evolved to blue by killing me. He was missing maybe 3 shield points, excluding the empty one from evolving. My damage should have dealt over 280 to him, with reduced pellet hits. Visibly he only fired 3 bullets to kill me, but the death recap showed I dealt nothing to him and he pumped me with a lot of rounds from the havoc.
With my view in recorded into the system, he probably would have been banned.
Has he been banned? Maybe, I did report him and put my reasoning in the chat. They do moderate the chat so typing your notes there is a good way to let them know why you did the in-game report.
I've also reported several people I've spectated when I was their bullets arcing.
Here's a better method of bullet tracking...
Server gets locations of people.
Server gets angle, direction, and speed of bullets and draws the path.
If person is in bullet path when bullet reaches them, it's a hit.
If person isn't there, it's a miss, regardless of if someone else's PC says it's supposed to be a hit.
Path tracking, not target tracking.
Only use target tracking if the gun fires missiles, like the Whistler.
So some of this bullet arcing nonsense is from the server itself, because someone else froze packets to shoot people and then released the packets to call hits.
It should instead track path, and because of their frozen packets they end up missing because they shot where the person wasn't any longer.
That's how it should be. More physics, less he-said-she-said between devices.
If you can guess where someone will be, and you fire, and they end up where the bullet hits, then it should be a hit, not a miss. It should also show that to both parties.
Kill Cam, see your death from your opponent's perspective. See their hacks, or the truth of how it works if it wasn't a hack. Maybe rethink your strategy so you can do better next time.
Should be easy to do if the server records everything.
For data storage saving, files can be deleted from the server after a month, though people should be able to download it in that case so they can keep the records of their matches.
Though keeping all of it would ensure you always have the evidence for all the bans you make.