The 50x cheaper (that's 2% of the cost, not 50% of the cost) number does assume 100% GPU utilization, which may or may not be realistic for your use case. If you're doing batch processing as part of a data pipeline, which is not an unusual use case, you can run your GPU at 100% utilization and turn it off when the batch finishes.
If you've got a highly variable workload then you're right, you'll have much lower utilization numbers. But if you work with an aggregator that can quickly hot swap LoRA fine-tunes (as a disclaimer, my company OpenPipe works in this space) you can get back a lot of that lost efficiency since we can increase/decrease GPU capacity only when our aggregate usage changes, which smooths things out.