While I understand your frustration OP. I feel that you're looking at this the wrong way. I had the same feelings when I first started. It was especially frustrating when I didn't understand how half of the game worked let alone how to stance dance. What I feel is the most common misconception when it comes to this game is that everyone has one specific role. This is not the case
Damage mitigation, Aggro Management, AND dps are everyone's responsibility. Dps should avoid being dumb and making healer's jobs harder (aka if you're more of a liability than an asset I will prioritize your raise last. nothing personal). Healers and dps should watch their aggro table and use cool downs as needed to avoid stealing aggro (you may have a higher ilvl than your tank. deal with it). And finally Healers and Tanks should strive to do their best to contribute dps.
However Where you are correct is that there is often times more emphasis placed on the last part as apposed to the previous two points. Many dps are quite ignorant in their duties and get mad at Tanks and Healers when they have to stop dpsing in order to adjust for dps. (insert laryzur meme here). If you get one of these dps (I often times do) and they start talking junk. Politely discuss with them why there's a problem and if they continue being jerks block them. They're not worth your time as a Tank or Healer. Also if a dps is doing exceptionally well or actually paying attention to mechanics Thank them and send them a comm. Positive reinforcement is the best way to promote good player habits.
That being said, I personally struggle to find a good balance between mitigation and dps and respect tanks who can do it well. But struggling is never an excuse to not practice a job you want to main. At the end of the day practice and mastery of your role in ALL of it's facets are what will carry you to victory