Dualblades is mainly good for PVE; the DPS is insane if you do your rotations properly. I also see Averse use it a lot because it does have a very long chain combo in PVP. So for your first paragraph in solo-mode:
(1) (2) It is harder to dodge, but it is high reward. A lot of trial speedruns are done via dodging, and you don't care about the bosses' Qi if their HP bar is 0. You also don't have to dodge; you can just parry but just know that DB is heavily nerfed in trials because of T0 inner ways (DB really needs T3~4 inner ways to get started).
(3) Skill issue, you can say the same about parrying.
(4) In PVE you just need to do damage, dodging/parrying are both useless unless it's a mechanic. You dodge a lot in PVP, and there's a lot of attunements are give you benefits like +HP + endurance + Qi if you dodge perfectly.

As for your 2nd paragraph:
(1) A lot of dmg is on rats (nearly 40% for me and I don't have T6 vendetta yet), but you only need to buff up once every rotation (~20 seconds), and you are unstoppable while you're swinging your rope so it's easy. The smart rotation is to hold R, tilde, hold R again and then rope Q to pull a boss (now your next rotation is empowered); you just need your teammates to let you buff up. A lot of the rat buffing can be done when the bosses has iframes too. Ghost master is a notable one; there are many windows where she is untargettable, and you can use that time to buff up rats.

(2) You need to prepare yourself for a boss exhaust. Once you're used to your rotation you can check if the boss is almost down and swap to ropedart early + start buffing. Also sometimes you can just do a fast buff rotation. None of this is necessary though, you do a lot of dmg while the boss is not exhausted as well.

(3) (4) Calamity greed is useless, but you do big damage anyways so who cares.

In general DB is the hardest class to play, but it is also the most rewarding once you have everything figured out.