Sturgeon was competent at enforcing party unity and winning Scottish elections. But in terms of actually achieving things for Scotland, both her and the SNP have failed. It's a one issue party so in terms of independence:

- Support for independence is now lower than when she took the reigns. That by itself must count as failure on the SNP's own terms.

- Lost the "once in a generation" referendum and then refused to accept the result, campaigning for years for a second referendum she had already agreed wouldn't happen.

- Made zero progress on reducing subsidy dependency on England, creating the widespread impression that the SNP doesn't really want Scotland to be independent. Many other specific issues around independence also have been ignored despite the lack of answers being one of the issues causing their referendum loss.

- Done everything possible to piss off the neighbours across the border, like encouraging anti-English rhetoric that would be considered grotesquely racist if there was a skin color difference.

And in non-referendum areas:

- Poverty and poor health are worse in Scotland than England.

- She said she wanted to be judged on closing education gaps, but they didn't close.

- The economy is worse.

- Social policy is totally reactive. Under Sturgeon the SNP just tended to copy whatever England was doing but making it more extreme, without any obvious guiding principles. The gender self-ID fiasco is a good example of that. 2/3rds of voters are against it and Salmond says it's done more damage to the independence campaign than anything else (which says a lot about the strength of that campaign). She didn't think through the consequences and when faced with the reality of what it means in the Isla Bryson case, flailed around and couldn't articulate a coherent response. Total incompetence.

- Scotland has quietly developed a reputation for corruption and weak institutions, with problems you don't see elsewhere in the country.

The nasty Salmond/Sturgeon affair was one example, and her resignation is likely triggered by the police finally starting to investigate where £600,000 of donated money was apparently embezzled to. The way she "can't recall" that her husband lent over £100,000 to the SNP is another symptom of this sort of thing.