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JBOD is not the same as RAID0

As far as data security is concerned, JBOD/linear combination and RAID0 are the same

With RAID0, you always need the disks in sync because reads need to alternate. With JBOD, as long as your reads are distributed, only one disk at a time needs to be active for a given read and you can benefit from simultaneous reads on different disks

RAID0 will always have the performance characteristics of the slowest disk times the stripe width.

JBOD will have performance depending on the disk currently used. With sufficient load, it could theoretically max out all disks at once but that's extremely unlikely and, with that kind of load, you'd necessarily have a queue so deep that latency shoots to the moon; resulting in an unusable system.
Most importantly of all however is that you cannot control which device is used. This means you cannot rely on getting better perf than the slowest device because, with any IO operation, you might just hit the slowest device instead of the more performant drives and there's no way to predict which you'll get.
It goes further too because any given application is unlikely to have a workload that even distributes over all disks. In a classical JBOD, you'd need a working set of data that is greater than the size of the individual disks (which is highly unlikely) or lots of fragmentation (you really don't want that). This means the perf that you can actually rely on getting in a JBOD is the perf of the slowest disk, regardless of how many disks there are.

Perf of slowest disk * number of disks > Perf of slowest disk.

QED.

You also assume that disk speeds are somehow vastly different whereas in reality, most modern hard drives perform very similarly.
Also nobody in their right mind would design a system that groups together disks with vastly different performance characteristics when performance is of any importance.