Although my answer doesn't revolve around a particular feature that is vulnerable, I think my answer will still prove helpful.

Hubspot is weakest concerning their pricing. They essentially ignore small businesses with their high pricing structure.

Mike Volpe, their CMO, basically admits this during his interview with me: https://www.growthhacker.tv/mike-volpe

That being said, I think that they are incredibly wise in regards to their pricing. Big companies have money. Big companies require less customer support. And higher margins allow them invest in the future instead of scraping my now.

Still, this is their weakness. It was also the weakness of KISSmetrics and Mixpanel appeared.