There are two listTasks calls included in web page. First one runs it with countOnly (for displaying total results) and second one actually retrieves data for display. Second is relatively quick in normal situations, first one is contraintuitively slow.

Aggregate function runs across whole table because of left join on users. This part could be dropped if countOnly is used, as left join is used only for retrieving user name and type, not for limiting query. Dropping this out reduces plan cost 33x for my db in generic case.