And this is the problem with your entire post; you undermined your points by giving them a sensationalist, edgy header, then make an entirely different point. "All inspirational advice is bs" is not in anyway the same as "don't use personal taste as an excuse to not improve". Especially when the "inspirational bs" is correct. The same way your forced diversity part isn't about forced diversity, it's about bad romance, which is not the same at all.
And (this is going to sound nasty but there's no nice way to put it) no one should take advice from someone who says art is objective. Art is entirely subjective. Now, there are aspects of art or writing that can be said to be objective, such as anatomy and spelling, but you can have perfect spelling all you want, if I don't like the piece, I don't like the piece, because taste is subjective. Just there are many terribly acted films that we love, or even non-anatomically correct animations or comics. Because art or writing are a culmination of their parts then presented to someone to like or dislike based on their personal tastes. The amount of times I've disagreed with judges and industry experts on things like portrait art awards, for example.
No, because it's happened. I've written really awesome (to me) complex plots and had people comment on them and then similar stories people ignore them for the ship. I revealed half the cast has been dead for chapters and got comments on the relationship not getting together yet or how unfair it was he was flirting with another man because he's got a boyfriend (who while endgame, they hadn't got together at this stage of the story) so I get that it's frustrating. But rather than whine about it, I go and look at what worked for one and what didn't work in the other. If the readers aren't taking away what you want them to, it's on you, not them. You're coming across exactly the same as those writers who yell at fans for shipping the hero and his rival who have an entire series full of chemistry and bonding, rather than the card board cut out love interest they shoved into a relationship at the last minute and didn't bother giving the hero any chemistry with, and think that's the fans fault rather than maybe thinking they should write a better love interest.