I'd say whether you're looking at it from a meta shifts standpoint or in a vacuum and not considering kits or the state of the game, it's gotta be the Snipewriter regardless. The ink consumption increase was a huge deal for letting it get three full charges from one ink tank with minimal Ink Saver Main gear, which is very close to enough for its special in a vacuum even after the nerfs. The movement speed buff was helpful for further improving its matchup against other anchors. The damage buff was arguably the most important since the state of the game has turned out to be more chip damage focused. I'm sure most of you know why but I'll go over what it did for those of you who aren't as in-the-know.
68 damage per shot is a big deal for a game that's centered around chip damage for reasons that you may already know, but in case you don't, picture the amount of relevant things in the game that deal 32+ damage and compare it to the things that deal 40+. For the former you have - Splattershot bullets, Squeezer bullets, Stamper horizontals, Rapid Blaster indirect, the outside hitboxes of basically every bomb in the game, plus I'm sure plenty more things I'm forgetting about. There's a lot. For the latter you have either of Dread Wringer's sloshes, Decav horizontals, and Splattershot Pro bullets, and none of those existed when Snipewriter came out. The list grew so much with that buff.
You could argue that some of its relevance is from Tacticooler's buffs, but for a while now people have been arguing that the 5B kit is also one of the strongest anchors in the game, with the only reason not to use it being that there aren't really any comps that it would fit onto any better than the 5H kit. This is despite it being stuck with Ink Storm which is not a very good special right now. This above anything else is a testament to how much better the main weapon's gotten - a technically bad kit on launch was enough to kill the weapon before, but now a technically mediocre kit is enough for the weapon to be seen as very strong. It's not just game state that's done this.