So "state-level actors wouldn't use pirated software" is not good evidence - they might, both because it's easy and to make it look authentic as an independent hacker. Whether independent or not, if you're good enough to gain access where you shouldn't, you probably know where to get safe pirated copies.

But the Russian name in the most recent save is still evidence, because it's a perfectly plausible slip-up.

DNC also said they believe it's a Russian intrusion, but we don't know if they rely on the same evidence for that - they potentially have access to a lot more.

Another thing is that Putin's government doesn't seem to be terribly concerned that you know they did something, as long as they can spread just a little doubt or have a fig leaf of plausible deniability. (Otherwise they'd probably not go around poisoning people with polonium). It makes sense if you view them as a sort of mafia: a mafia boss may not want it to be an official matter that he killed some people who got in his way - but he sure wants similar people to know.

EDIT: Let's assume Russian state level actor, and that the purpose of the hack is to obtain evidence that will lead to an indictment of Hillary, improving Trumps chances at winning the presidency (a Trump presidency would presumably be very susceptible to strong-man optics and influence form the Kremlin). First strike against that, is timing: You want Hillary to formally secure the nomination first. An (imminent) indictment against the presumptive nominee would surely allow some kind of manoeuvring to hand the nomination to Sanders (or even someone else) in a way that can't be done after the convention is wrapped up. Sanders/Trump is probably in Trumps favour, but not as much as indicted-Hillary/Trump is. Second strike is the publicity. Being hacked, especially by a malevolent foreign power, has several positive PR spins, standing up against foreign interference in a democratic election etc. If you just wanted to hit Hillary, make it look like an anonymous whistleblower from inside the DNC leaking documents to an investigative reporter (Russia certainly has the capacity to make such a plant). Best not to have Russian fingerprints at all on this.