not a past graduate
but i'm doing the exact same topics as you... ken webb's stuff is decent for summaries but imo in terms of learning new content and studying in-depth it's like 'go girl, give us nothing', HTA is really good for filling in gaps in my notes when i'm done with the bulk of them, apart from the core study chapter... thing is there's no perfect 'one' textbook, and in my opinion apart from modern history transformed every single other textbook that covers several of the topics in different chapters sucks. here's what i used for those topics
power and authority: power and authority: investigating and interpreting the sources (info is mid but the sources are good, you can use the qs they give you and make your own practice qs based on the hsc and trials), i thought HTA was actually good for the info. my teacher also gave my class readings from hitler, stalin and mussolini by bruce f pauley and those were really good as well. for the nazi germany bits it's also really easy to find good readings and info from the us holocaust museum and the holocaust memorial day trust)
soviet union: russia under tsarism and communism, 1881-1953 (best textbook ever, has everything, so much info with impacts/assessments/historiography and quoted sources; it's not a hsc-focused text but it actually covers every dotpoint of the soviet union syllabus), stalin's russia, 1924-53 by michael lynch (also very good, info is so easy to read and understand, he's also a historian so historiography) my teacher also had various readings from the following books that i found had the most useful and helpful info: stalin and the soviet union (stephen j lee), everyday stalinism (sheila fitzpatrick), stalin (dr kevin mcdermott)
cold war: contested spaces: the cold war (very good, has so much historiography, best hsc-focused textbook ever since it addresses every syllabus dotpoint directly), the cold war and beyond: us relations with soviet and post soviet russia by james fitzgerald (also very good, one of my favourite books to read about the cold war, also tons of historiography but also some added analysis of stuff and arguments)