I agree the lack of cosmetic filtering by default is a problem, so I've contributed updated filters to EasyList to hide sponsored post containers, the sponsored sidebar section, and any takeover banners; this is awaiting review by EasyList maintainers, but in the meantime you can hide sponsored post containers by enabling AdGuard Base in uBlock Origin's filter lists.

EDIT: Due to the recent frequency of Tumblr regenerating their classnames, Anti-Capitalism has now been added as a feature.