I mean......

if we're questioning Sasuke's redemption we have to question Gaara's. Because he was 100% psychotic murderer the whole way with very little to indicate his redeemability either- Gaara was technically more evil in some ways because he didn't want to kill a specific person for revenge, he just wanted to kill people in general to prove he existed- and actually killed a few genin during the exams, unlike Sasuke who even after training with Orochimaru for three years was specifically not killing people who weren't Itachi. and yet Naruto redeemed Gaara earlier. So like, if Sasuke shouldn't be redeemed or was poorly executed, then we have to question Gaara's redemption. oh and Pain, Pain is technically worse than Sasuke because Pain actually killed Naruto's whole village, so we have to question if Pain's redemption was good as well. and technically all the deaths that Sasuke did achieve was against people who either self-destructed or let themselves die because of a disease. so its kind of questionable if Sasuke truly killed anyone?

that and Sasuke has an arc/novel after the finale called Sasuke Shinden: Rise of Sunset. its a story all about him and he does things like: spare the villain because they suffered injustice because of his clan in the past, help free slaves from fighting in a coliseum and such.

also we have to take into account: Naruto world isn't our world. its a world of ninja villages who have been at war with each other for generations, he is not some modern kid facing all the same issues normal kids do, he is kid born into a military-based town whose entire history is fighting three continent-spanning wars with periods of peace in between which is considered an improvement over 900 years of constant feudal warfare with less tech. there is probably tons of stories in his world about ninjas from centuries past and the village era taking revenge for their fallen comrade or clan mate and it not only being accepted but maybe even glorified and used as propaganda against other villages who are Konoha's enemies so that he doesn't feel bad about killing the enemy, probably with further propaganda about traitors which y'know, militaries generally never like and Itachi committed a quite big betrayal to his entire clan. can you really blame Sasuke for thinking revenge is the solution, when there is an entire culture of warfare built on a thousand years of conflict pushing kids to become weapons for the state?