Comment by Analemma_

It's important to fix vulnerabilities even if they are blocked by the sandbox, because attackers stockpile partial 0-days in the hopes of using them in case a complementary exploit is found later. i.e. a sandbox escape doesn't help you on its own, but it's remotely possible someone was using one in combination with one of these fixed bugs and has now been thwarted. I consider this a straightforward success for security triage and fixing.