A weapon like that would suffer a major inflation in strategic value if exposed through overuse. The Dominion might simply be much smarter than the Alpha Axis, and treat its cloakships like the Allies treated their Ultra intel decrypts in WWII, putting a lot of effort into hiding the very existence of the capacity.
(In contrast, the Defiant was probably given the crappiest cloak in the Romulan inventory, so that there would be little chance of the ship hiding from Romulans. Swapping that for a more capable Klingon unit might not have been worth the effort when it turned out Sisko did not have infiltration of the Romulan Star Empire topmost in his mind after all.)
Timo Saloniemi
The Romulans wanted to know as much as possible about the Dominion, just like the Federation. If the Federation is willing to risk their ship and crew to find out, and they have a Romulan officer aboard making sure they're not holding much back, they'd let the Federation use a good cloak.