I've had the same thought, and yes, it would be throttled as described.
One way that I wanted to solve this was to implement real-time file placement rules that would place new files on the pool and then move them to the cloud drive in the background. These kinds of rules would essentially allow the pool to act as a level 2 cache over the cloud drive. The problem with this approach is that now you're requiring periodic background balancing, which I would like to avoid because it doesn't scale. But I've actually gone ahead and implemented this to give it a go, and then ended up rolling it back because it was 1. too complicated, 2. the performance wasn't up to snuff.