No it's not. Where are all of the Stagefright exploits? This was supposed to be Android's security armageddon according to the scaremongering bloggers. And yet nothing happened. According to Google's telemetry of over 1.4 billion phones there has not been 1 case of a Stagefright exploit in the wild. So your assumption that Stagefright is "trivially weaponizable" is inconsistent with your knowledge of Android security and mitigations.