Realistically support for more than one browser engine is going to increase security in aggregate since it would implicitly decrease the impact of a vulnerabili

Realistically support for more than one browser engine is going to increase security in aggregate since it would implicitly decrease the impact of a vulnerability. This has a compounding effect where a zero day for Safari would become less valuable on the black market and therefore become less incentivized to a degree. To give an example: A single Safari engine bug could compromise all iPhones, but if the market share was say 50/50 with Chrome, then the impact of a security vulnerability would now be halved.