We have no plans to change the rarity of characters.
The only real answer right now (other than killing it) is the Prisoner, because nothing else has Passive Block.
You're not accounting for attack team usage, but even if you only account for defense team usage, he's still the go-to Warrior to the exclusion of nearly every other non-Eddie Warrior in the game.
Ultimately, the adjustment here to his Attack is not that substantial; he's going from effectively tied for best maxed out Attack in the game to being higher Attack than every character that isn't basically tied for highest Attack in the game (from approx 1750 to approx 1500 at 5 star level 100). We really are just trying to give other high-Attack-focused characters a bit more of an edge without power creeping everyone else above him.
We definitely don't want to change Invisibility in that manner, as there's a high risk of something unintended going through (either a bug which causes more problems or a possible OP combo when trying to abuse Extra Turns). He can be a bit unreliable on defense, but we nonetheless would like to see him more on offense and defense, and these changes we think will help push him in that direction.
We definitely expect him to still be a popular character, but the reduction of free damage from his shields will mean he's a more passive and defensive character, and the increased reliability of other passives means we hope to see other defensive options be potentially more synergistic with your team depending on what characters you're planning to use.
Whoops, good catch. We'll make sure that's correct in the release patch notes.
There's definitely a bug where augments like Void Shields are proccing more than we should, and we aim to fix that as soon as possible, but it's a tech issue, so I can't make any guarantees.
That said, we feel that even if that were in order the real threat of Void Shields is it's removal powers while also reducing damage to your characters, so we feel that softening the reflected damage is an appropriate action to encourage use of other purple talismans.
Removing his Reflect Shield as well was definitely considered, but realistically, damage from Magma Shields on characters who survived was way outstripping the damage that reflect shields could ever hope to do. We feel the random allocation of 1/3 of the time having a damaging shield instead of 2/3 is a fine place for him to be in.