Disruptor is a hero that requires you to have an intricate knowledge of enemy heroes, and also requires you to have some exp to go around the map making kills happen. You don't really bring the damage as much as a typical hero, so make sure that you setup with your allies help.
If you are a solo support with carry versus a solo offlane hero, make sure that you contest his exp so that your carry can eventually go 1v1 with that hero and threaten a kill without you having to be there.
Also, please buy Urn on support heroes! It's one of the most cost efficient items in the game!