i don't think the last episode retcons the drop in 105 at all. the influence of akasha's blood was already implied in seasons 1 and 2 (and this was part of fandom discussions at the time) and according to sam, in an interview far before s3 was in production, lestat was supposed to reference akasha's blood while lestat and louis are in the sky. hence, this is not something they just threw in to make lestat more sympathetic in reaction to fans, but something that has been planned since the beginning; so it cannot be a retcon.
on top of that, lestat is not saying this to absolve himself of blame. it is clear he still feels shame and regret over what he did, he says "this is the hell i unleash on all those near me." he was influenced by the violence of akasha's blood, but he still dropped louis and he took that on during the trial, which is a scene that has not been disputed in any way. at the point of the drop, lestat has had akasha's blood for a mere 30 years. and in the aforementioned interview, sam also said that the toxic, abusive rage that lestat has is coming from an extreme, monstrous power that he has no idea how to control, that he's trying to repress all the time, that his already volatile nature gets triggered even further by this power. this does not mean that lestat is not capable of violence, but that akasha's blood pushes it higher than it would be without it.
in the end, i don't think the show is saying "well, lestat is blameless now!" the way people are interpreting it. this is far more similar to what we see in 207; adding complexity to the whole fight between louis and lestat but still foregrounding that it was lestat who made those choices and has to live with the regret of them forever. it's how lestat is trying to communicate that there is something monstrous inside of him that he cannot control, that he should not pass on.