Coincidentally, I've come up with half your fixes on my own and been thinking about them since DRK and Dark Dance came into play, but sadly they're mostly technical game system changes. As such I don't have hope they'll ever be fixed, which is just sad. For reference, I mean really stupidly obvious things that are ridiculous for having not been implemented from the start like:
-Every single incoming attack on a player should be parryable/blockable from every single side but the rear (Not exactly what you said, I know)
-Every single enemy should be Blindable and almost every targeted attack should be able to miss/be dodged, starting at a 0% floor (Obviously one-off, powerful attacks have to 100% hit or survival would feel too random)
-Only weaponskills part of combos, and nothing else, should ever break a combo (For tanks only)
-Abilities should always be affected by healing modifiers (I'd even be okay with Mantra+Second Wind on a Monk, the recast times are more than prohibitive enough)
The rest of what you said is more about game design than game systems, so I won't bother going into that but to say that I agree with all of it wholeheartedly except one thing. I respectfully disagree that Oaths/Grit should be on the GCD. Even if they were affected by Skill Speed and didn't break combos, it shouldn't feel like an awkwardly punishing thing to switch to or from tanking as a PLD/DRK. In fact, in my opinion it's a completely stupid and archaic thing for "tank stances" to even directly reduce damage at all. They should simply limit damage output through other methods. However, that's another topic. :P
