Breaking from dots was a risk to be sure.
But that just means you needed to find other ways to use it.
One way I liked to use it is to pre set up feathers and then I can use Spectral Guise and run into my feathers and you can cross the map a long distance before loosing stealth and pop out the other side.
Worked great to get behind enemy lines in battle grounds and Ashran.
Also you can Mass Dispel yourself prior to shielding and then Spectral Guise. Of course if you’re poisoned or bleeding, then you had to deal with that another way via an item or someone else removing it.
You can also time it so a warrior can charge your Guise or a Death Knight will grip your guise instead of you allowing you more time to play keep away and get your dots out.
You can use Spectral Guise and walk in a hunter ice trap and you can be stealthed while frozen.
There are some others I can’t quite recall as well.
I think the PvP video Anboni made in WoD shows a lot of opportunities of Spectral Guise use and why it can be such a good spell and still in today’s modern game can find such uses once again.
You can find his vid in this link below alongside a link to my thread showing other videos of Shadow prior to the removal of both Spectral Guise and the addition of Voidform.