Passing collections of subtypes where a read-only collection of supertypes is expected by the receiving code is fine, because the receiving code can't do anything that would break type safety.

But Java decided to only have a single array type, as a matter of expediency. But they also wanted covariance, because, as you point out, sometimes it's just convenient - more expediency. And so the trade-off was to enforce safety at runtime.

It's still a defect in a sense that the design itself could be made sound, if there were a read-only array reference type in Java.