Was there manipulation or interference with the Capitol police or other first responders to increase a state of vulnerability to make the attack on the Capitol successful?

This is very true and, as you know, a standard operating procedure for causing events like this. They manipulate and maneuver people to soften the target, so to speak, as they do not desire for there to be a death toll in most instances unless that is the primary objective for purposes of social unrest and creating political distractions and the undermining of institutions, and so on. Outright killing is a too severe outcome to be useful in many cases, so there needs to be a moderate level of pressure with minimum risk to personnel who, after all, are valuable as a weapon and are not considered cannon fodder. They are still expendable, meaning they are put at risk with little concern for their welfare, but with an expectation that these lower-level exercises will be valuable for training and not a suicide mission.