The UN is as effective as its members want it to be. Rigth no wit serves the interests of the US and other powerful nations to have a weak UN so they can do what they please and still have a scapegoat for when things go sour.
As far as PMC being more effective then UN peacekeepers, thats not true. I actually did a paper on this topic. UN Peacekeepers are again, only as effective as the militaries they come from. Bangladesh is the number one contributer to operations, so obviously they are not as good as the USMC. There have been some who have advocated for the use of PMCs in the short run until members are able to mobilize their own forces to replace them. PMCs can mobilize a battalion on about 2 weeks notice, Member nations could take several weeks or even months. So deploy PMCs immediately and wait for the calvary.
PMCS are nto as kickass as some believe though. Most people in PMCs are Tier 3 contractors, that is made up of ex-military of developing nations or less. Tier 1 which is SEALS, SAS, JTF-2 etc. make up only a small portion of the contractors PMCs deploy (including Blackwater). Tier 2 is developed nations military, police etc or people with advance skill sets of a similar nature.
EO was mostly Tier 3 with some Tier 1 commanders for their operations in SL.