From my understanding, MV3 kills vital features of ad-blockers in that

1. Some filtering rules do rely on the ability to read the content of the webpage, which can’t be migrated, per the FAQ linked in the article
2. The declarative API means updating the rules means an update to the plugin itself, which might get delayed by the reviewing process, causing the blocker to lag behind the tracker. It might not be able to recover as quickly like in the recent YouTube catch-up round.