Oh, but it is. We only have Mengsk's rhetoric to go by when he uses Duke as an example of the Confederates being failures and to justify there removal. After that was accomplished, we still only have Mengsk's rhetoric moving forward. That Mengsk then goes on to lose to the UED and then finally Kerrigan's Swarm is due in part to his incompetence and his initial action of removing the Confederacy.
Why you say? Well, we need to dive into hypotheticals here but there is the possibility that the Confederacy may not have fallen (or lost as many as 9 out of 13 of their coreworlds) had Mengsk not taken his drastic action with the Psi Emitters. If Mengsk was removed from Sc1, it is possible the Confeds lackadaisical regard toward the Zerg was because they already had a plan to control or redirect them away.
The Jacobs Installation is testament to that scenario but because Mengsk does exist, the revelations there are twisted by Mengsk to fuel his position and eventual actions. So, if the Confeds could keep the Zerg at bay (since they would also have to contend with the Protoss, too) to maintain the strength of their coreworlds, they would have stood a greater chance at potentially resisting the eventual UED arrival as well in comparison to the actual series of events we got in BW where the UED fought against a government built up from the remnants (caused by a Zerg's surgical strike that would've never happened if Mengsk weren't around) of the previous one and
may have partly succeeded because of that. Lastly, the Confeds wouldn't have to deal with what happened in HotS, because Kerrigan's revenge action was a by-product of Mengsk's actions on Tarsonis and if Mengsk was out of the equation then Kerrigan would be, too.
As you can see, Mengsk is the pivot point for all these changes in the government and the reason for all the subsequent turmoil it had to experience.