Yes, Duffy's leaving Warwick Avenue in the video, even if that doesn't fit with the song (where she's on her way there). But they decided to capture the emotion, and to the listener, now the lyrics
can mean something else. It can now be that Duffy's retelling the story to the viewer in a taxi, for example, though that's not how it was intended when shot.
And yep, I'm a Janelle fan, though no, the video isn't specifically about her being put down for being black, it's part of a concept album theme she's developed. It might be influenced by race, yes, but like any interesting form of art, it doesn't have ONE meaning behind it. That's just taking it at face value as the video itself. You're entitled to that view and it might be partially right, but it won't be the sole correct one.
That being said, I don't understand the point of calling her "another neo-soul/old school singer" (as if it's a bad thing, too) when 1. there are plenty of people in every genre before everyone... ever, 2. you're unaware of what she's expressing, but are quickly judging by the first impression you get, proving my point. I'm not offended, just confused as to why mention all that, really.
As for LM being about someone else... I never dismissed that idea:
"With her movements, I think she's either trying to live with herself, put the pieces of her "soul" back together or
fighting with someone/something that's tortured her for a long time."
To me, the lyrics could just be vaguely referring to ~someone else~ while really referring to the other side of her (see: the video). She is still singing to someone, it's just another version of her. It's not like the budget was so little that they couldn't afford a man to sit on that chair, or have a mannequin silhouette or something

Or so I hope lmao. Only she knows what she really means in the song and why she expressed it this way, but to dismiss it as "trash" and her "new low" seems like such a gross over exaggeration given her track record with some of her music videos lately. And none of the reasons you gave (iPhone, DIY, cheap dress) make a video trash, especially if the end-product meant something to someone--and while there are people that disliked it, plenty of people really loved it too. It can be trash to you, but it's not "really" trash, like you so definitively say.
I'm happy the video didn't go for the obvious, even if it was because of budget or for a specific reason. I could be wrong about the intentions, but my interpretation/projection won't be, which makes art interesting to me.
However, I'll agree, the most disappointing part of the video for me is that the song wasn't mixed properly. -___- I love the general idea song and it was fine for the single, but what is so hard about getting a real drummer and a good mixer for the album version? That screams budget issues more than the video to me, which was just done spontaneously and didn't go through a huge planning process (that doesn't mean I think it didn't have any thought btw haha.)