I have moved to the left on this sort of issue after there was no high level official response or remediation after the Snowden revelations. I think many people fail to grasp how vulnerable we are to surveillance and propaganda. I have not seen any elected officials offer any reasonable reassurance or even accept accountability for what appear to be excesses. This suggests to me either fear or complicity, either of which are pretty bad news.

I think your questions contain the assumptions for my answer:

A state sponsored intelligence agency has the sophistication to forge the IOCs (or not to). Russia has a state sponsored intelligence agency. Therefore, the IOCs would not have been found unless the state sponsored agency responsible for the leak wanted them found. Thus if the data was leaked by Russia, it would have been accountable only if being held accountable offered a strategic benefit.

I have not yet observed any strategic benefit to Russia doing this. In fact, unless the hypothetical smoking gun is so significant that it will harm the very likely election of HRC to the presidency (and that was deemed beneficial), I find it unlikely that Russia would have been willing to risk the significant harm in diplomacy caused by being caught meddling in a US election.

So I think the hack was either done by a less sophisticated group (likely Russian) or by a different state sponsored group who chose to leave the trail pointing to Russia. Considering that escalated US/Russia tensions will amount to Billions in appropriations, there is clearly a financial incentive for stewing the conflict. There is also a dedicated interest group in the US that has tried to nudge the US into more direct conflict with Russia over the Ukraine, etc. But the surprising factor has been how readily Clinton's campaign jumped into finger pointing.

I do not see how it possibly benefits Clinton (or her diplomatic core in 2017) to engage Russia in finger pointing and accusations of meddling in a US election. If a response was warranted, it should (in my opinion) have been measured, and it should have come from president Obama, and the issue should not have become a rallying cry for HRC's campaign. It's absurd and unprecedented for a candidate who does not hold office to levy such serious accusations at a foreign government. If accusations are warranted there is an existing group of officials whose job it is to deal with it.

The first version of the Russia finger pointing story didn't really get legs and was not vetted by any named/credible infosec experts. The second round was, by the firms you mention, and I believe at least one official made a statement confirming the suspicion of Russian involvement.

So there is some unknown motive for HRC deciding to circumvent the proper diplomatic method of resolving something as serious as election tampering by a foreign country. I doubt it amounts simply to trying to leverage the news cycle in a beneficial way, or even misdirection. It seems like too big a risk, one that a former Secretary of State would be abundantly cognizant of, especially if it really was Russia and some retaliatory action would need to be taken in the near future.

I think there is room for exploration of the various motives that other state actors might have had for leaking the docs, but my guess is that the goal is to get the information into public view so that it cannot be used against HRC later after she's elected. Only if the leaked information ends up containing an election-risking smoking gun will it be plausible to believe that a state actor released the information to harm HRC.