So, by way of background, I began my adult life as a painfully earnest member of a Trotskyist wish tank. The version of Soviet politics I learned back then was: Testament of Lenin - Lenin Dies - Something Something - Oh Noes! Police State! The Forces of Reaction have prevailed! - Trotsky's Exile - Icepick. The implicit assumption in this chronology is that Trotsky had the correct revolutionary program and would have won his rightful place as leader of the Soviet Union had it not been for Stalin's underhanded machinations. As I got older, I heard other partisan accounts of this that suggested that Stalin actually won an honest victory, an honest majority of the CPUSSR because his political program was a more appropriate response to the domestic and international realities of the mid-20s. So where can I go for accurate, reasonably objective accounts of their post-Lenin power struggle and the politics involved? I am looking for material from actual historians, published by academic or commercial presses. I am not looking for material published by newspaper cults or anyone with an axiom to grind. Thank you for your time and assistance.
I suppose you might want to have a looke at Stephen Kotkin's Stalin biography. Kotkin grants Trotsky his due - for example noting just how important he was to the success of 1917 revolution and the Civil War - while also acknowledging his faults and where it all 'went wrong'. By its nature the book also goes into just how it was that Stalin 'won'. I think it was in interview that Kotkin emphasised that he doesn't like Stalin but that he was awed by his achievements given his humble beginnings, so I think that might be neutral enough for your purposes, or at least not leaning too far into Stalinist territory.
The only caveat I would add is that Kotkin's book almost assumes you're familiar with Soviet history, but given your interests you probably know the basics well enough. A more baseline but less interesting starter might be Robert Service's book on Stalin. Also big chunks of Kotkin's bio were about 19th/early 20th Century history with Kotkin trying to provide context (and fill in some of the chronology/space where supposely not much was going on with Stalin). But equally he does have the occasional interesting point in these sections so you might still get a kick out of it.
Depending on which components of Trotsky's revolutionary program you saw as more correct you might also be interested to know that volume 2 of Kotkin's biography will focusing more on the great break, collectivisation etc. If you're more interested in the internationalist aspect the first volume would be less relevant though it does touch on Stalin's policy towards the KMT in China.