Alternative browsers would introduce other security concerns, including JIT. It’s debatable whether that would be a net security gain or loss, but it’s silly to just pretend it’s not a thing.
Security as the product of multiple risks.
Discovering a new risk does not mean all of the other ones evaporate and all decision making should be made solely with this one factor in mind.
"Decreasing the security" is not binary thinking. It's just a fact today. Also, ability to run software doesn't make you less secure. I never saw any real proof of that. It's the opposite: Competition between different browsers forces them to increase the security, and it doesn't work for Safari on iOS.
I think a detached and distanced perspective must come to the conclusion that vendor lock-in isn't healthy. For security, performance or flexibility it tends to fall short sooner or later.
One could also talk about the relevance of a speculative attack that hasn't been abused for years. There can be multiple reasons for that, but we shouldn't just ignore the main design motivation of Apple here. That would be frivolous and that excludes serious security discussions.
Alternative browsers would introduce other security concerns, including JIT. It’s debatable whether that would be a net security gain or loss, but it’s silly to just pretend it’s not a thing.
Security as the product of multiple risks.
Discovering a new risk does not mean all of the other ones evaporate and all decision making should be made solely with this one factor in mind.