In the most simple terms he was a corrupt politician who tried to amass more and more power for himself using populism and extra-legal repression. Both of these methods put him at odds with party rule and the rule of law. There is no reason to accept these aspects of his governance when the CPC under Xi was able to push through the same kind of leftist reforms eventually while doing everything by the book at the same time.
The problem with populism is that it's absolutely possible to use it for counter-revolutionary purposes. It should never be forgotten that every ideology needs a political structure to be for it to be implemented and every revolution produces a new elite. Attacking an already existing socialist political structure under any kind of slogan endangers all previous achievements and, in the end, no matter the intentions of particular leaders, the question of who benefits must always be asked when talking about a political restructuring.
Both Bo's mentor and right-hand man who ultimately betrayed him directed security forces. In a country where the encroachment of capitalism primarily occurred through the erosion of rule of law, wouldn't extra-legal repression have empowered the same kind of corrupt structures, and even worse creating a patronage system that can rival the official party structure?
It's possible that if he was successful in taking power, he would've created a short-lived leftist (intra-party) dictatorship, which then would collapse into a counter-revolution against the party by his cronies.
Such figures are known to exist in communist history. Tukhachevsky and Lin Biao are thought to have planned a coup against the party using the military. Both were leftists. Worse, there is Andropov whose career was followed by both the appearance of dissidents and their repression as the longest standing head of the KGB. When he was the ambassador to Hungary and the Hungarian Revolution transpired, shouldn't he have been demoted instead of being promoted for its repression? Couldn't it all have been planned by him, when shortly after ascending to the position of general secretary, he was followed by Gorbachev, who went on to dismantle the USSR? As the former head of the KGB, shouldn't his personal appointments as general secretary have been more than exceptional? Why didn't he see what was coming?
>>2827760That affair begs the question why he was in contact with a likely MI6 agent in the first place.