I thought it was a bit daft that Voyager never bothered to develop a cloak, which would have been really useful sneaking through the Delta Quadrant. It's not as if the Romulans would find out. The suggestion must be that the Federation really don't have much experience at all. They might know the basic theory, and have a few captured examples, but haven't been able to make them work in practice due to the treaty. The Pegasus attempt was clearly very, very secret.