From watching through it once I noticed a few things you could improve on as a start. I'll just focus on the 'major' things (not so major really) for a start, as I believe practice should always be centered around one aspect at a time. Once you've mastered that aspect, move on to the next.
- Positioning: Often left unnoticed, positioning is a very underrated mechanic. I noticed quite a few times in the video that you would run up close to a foe to attack him, even when the staff was equipped. While this is not necessarily a bad thing, optimizing your positioning on the battlefield can drastically increase your overall efficiency. In the case of your bunker build, your job is not to deal damage, but rather to stay alive and supporting your allies (which you also did at times). Being up front only brings you in unnecessary danger, and is rarely really beneficial to your allies. (Point of reference: ~5:50)
- Managing cooldowns: While it can be difficult to properly calculate, minimally using your cooldowns is the key to forcing sustained enounters. Mostly noticable at 3:50, a single stun-break + SoR before stomping would have done the job, leaving you with 2 cooldowns left.
- Optimizing dodges: I'd probably estimate this to be the most important aspect of competitive Gw2 play. Optimizing the use of dodge to mitigate as much damage as possible while still maintaining decent pressure is what will win you duels. I've duelled quite a lot with some of the members from [PTC] and some from the other top teams, and often what determined who was the winner in the end could be broken down to a single dodge. Take a look through your video, and whenever you dodge, pause the game and consider if that dodge was necessary or if you should have saved the endurance for a later dodge. This is where knowing every other class and their abilities comes into play. Achieving perfect dodging is very much impossible, but paying attention to it makes a huge difference.
Those are the 3 major things that I think you could work on. I noticed some minor stuff as well (although some of them are essentially just minor disagreements
- Light of Deliverence is good, but so is Heal Area and the other skills the book offers.
- When you're kiting, consider just running forward, as running sidewards is slightly slower, giving your enemies the opportunity to catch up with you (~13:30 against warrior). Couple with Heal Area and Swiftness and your opponents will rip hair out. Also, run in big circles, as that prevents your opponents from running in a smaller circle, still being within attack-range.
- Virtues: Virtue of Justice should always be on CD. Especially in team-fights. Virtue of Courage is a 5s on-demand protection buff for your team. Much better than 1 block every 40s.
- Build: I personally prefer greatsword alot more than staff. Honestly, I think the staff is an extremely inefficient weapon. Greatsword provides retal to your entire team (very consistently if comboed - which the greatsword has tons of options for).
- Consider your positioning on the map: If your team is winning a point, you shouldn't stay around, as you're not contributing much. Bunker guardians are more of a 'lone-wolf' class than a team player honestly.
With all that being said, you honestly shouln't expect to gain much running bunker guardian anymore. A properly played meditations guardian (0.30.30.5.5 or 0.30.30.10.0) has about equal survivability and a much higher damage output. Keep in mind that this is personal opinion, and I'm sure a lot will disagree on it, but this is my experience playing the guardian, and something that many of the high-tier players whom I've played with agrees with.
Anyway, hope you can use some of these observations. Good luck in your efforts.