It's not unique to Apple. And we should take security seriously. To people who are technically literate and think they can navigate security risks it's not a big deal but people's entire lives are frequently turned upside down by scams and security loopholes
An average user can't dive into the bluetooth driver code and figure out where in the 4000 page spec something deviates and is now a security issue. So we have to assume the worst.
Go look at the CVE's for iMessage, plurality of RCE's on apple devices in the last decade is Apple's iMessage implementation, and it's their own protocol! And almost all of the rest are apple's implementation of the open web standards!
Even with that (large) Apple security group, iMessage is difficult to lock down properly, as you note. However, I think that the cost of 0 day subscriptions for iOS vs Android tell a pretty good story: iOS zero day subscriptions sold to intelligence agencies/governments cost roughly $1mm / seat (phone compromised). Android -- $10k.
There are many many decisions along the way that end up with that raw 100x additional cost for iOS security breaches -- value Apple delivers to its customers when they purchase iOS products.
You cannot pick and choose from the outside and know which of your preferred opening-up implementations would impact that cost. My argument is that opening this up is one of likely hundreds of possible decisions that would contribute to lowering that cost of exploit.
