Based on my observations, players can gain all 8 provinces rather quickly if they need to, such as when they play against someone going for an alt-VP strategy. Imagine, we're talking about BMU in this article. Most decks have action cards in them. Yeah, action-density decreases as players get more Provinces, but not by that much. Players might still be able to pull off cool things with Mystic + top deck inspection, or they have Cartographers, or maybe they just have smithies.
I think the most important lesson to learn from this article is that you shouldn't buy Duchies on a whim, and that you should not forget the power of Provinces. Sometimes, we get too caught up on how great Duchies are.