One reason is that transaction performance could be very different, even regardless to data volume.

Your points are all correct of course, but then that wouldn’t be a preview environment, would it? It would be shared database state in a database staging environment.

Which, for what it’s worth, is also how I have seen this problem managed when it came up.

As for costs, maybe true, but it could also take a lot longer than an hour to bring up a large deployment. And if every engineer is doing this for one hour a week, and you have a few dozen engineers, there’s a 2x cost increase with a tougher capacity planning problem since your load is now tied to your hiring plans.