The thing is, the long stretches between seasons should mean more time to write and refine scripts, better ideas, writing etc. That hasn't been the case since they started these long gaps during Matt Smiths run, and it has progressively gotten worse. Some Later Matt smith scripts are dreadful, and as much as I love Capaldi's performance, many of his had enormous gaps but still making mediocre scripts at best.
More importantly we haven't had a 13 defining speech or moment yet. Where's her Pandorica, 11th Hour, Zygon Inversion or Heaven Sent speech? There was a start of a "I am the Doctor" heroic speech in Villa Diodati, but it was brief and promptly forgotten, back to her reacting to the cybermen, reacting to The Master, reacting to Ruth, reacting to the destruction of Gallifrey.
I don't doubt her acting ability. Its the writing, it's always the writing. Ask Colin Baker.