The points made in that blog article are understandable. However, UNESCO (like the other UN entities) is a political grouping of various member states, and does not really have the power / the will to rock the boat - and ultimately to change anything. Contrary to other international bodies (such as the WTO or the UN Security Council - when the latter is in agreement) it cannot issue sanctions apart from deleting a site from the WH List (which has no consequence for a member state except in terms of reputation, and does nothing to help the site in question). Furthermore, due to its antics in other areas, it has no budget to actually really help maintain any of the sites on the WH List. Instead, it has over the years refined an ever more complex list management bureaucracy - even for the flagship World Heritage list - which has vastly increased the burden of nominating a new site, especially for poor countries (consider e.g. Madagascar this year, comparing to the millions the Chinese apparently spend on each nomination). Its periodic review can help raise awareness for deteriorating sites or planned constructions that would have a negative impact on the site (St Petersburg comes to mind), but it leaves the real assistance to NGOs or to member states.
Is it UNESCO's fault? Under different management, it could have been more assertive and more impact-driven. But given the political games in the background, maybe we all just expect too much of it.