Which is exactly why you periodically do maintenance to compact the free space. Thus it isn't an issue in practice unless you have a very specific workload in which case you should probably be using a specialized solution. (Although I've read that apparently you can even get a workload like postgres working reasonably well on zfs which surprises me.)

If things get to the point where there's over 1 TB of fragmented free space on a filesystem that is entirely the fault of the operator.