Only saw half of the video.
First of all, don't 2 man and 3 man cap an empty point.
As a thief your main focus should be decap points and +1 on fights.
If you want to play d/d and I advice against it since it requires more skill than d/p, precast cloak and dagger to f1 and than backstab.
With d/p you do 5 + 2 and at the mid of animation f1 to backstab, or 5 + 2, and 3 to backstab.
am I watching beta footage? I only watched a couple min but here are some obvious flaws.
you stealth way too long and don't do anything for your team, you sneak attack with short bow in point blank range, you aren't using daredevil, you never use your skills, shadow refuge is useless.
you don't teleport to mid with shortbow but run up instead (you can infiltrate arrow basically anywhere there), you aren't using dagger/pistol, and a thief should never stop moving. I'm gonna take a wild guess and say you never decapped once, and I cringed when you didn't swap to dagger at least to kill that warrior in the beginning, you could have heartseeker+steal to down him. steal will also port you up to mid with a target.
you stand in aoe for no reason
ctrl+space is also a very odd keybind and I imagine will be hard to combo with other binds, all I can suggest is watch pvp videos on youtube cuz you seem to be new to the game not just thief.