The first image, in my opinion, it is "bitter" mustard greens, not general mustard greens. So, That's really bitter in taste. We usually eat bitter mustard greens with spicy chili sauce to serve rice to reduce the bitter taste.
Hope you can see the bak choy can be harvest. In my back garden, similar with you, the bugs attacks always. So, for now I never grow green leaf in back garden.
I thought the position is big role to avoid bugs. Also, in the future, you can start to plant flowers like marigolds to attarct bugs.
Marigold is definitely on my list of plants next year, hopefully but will help. The bugs here seems very strong, I've seen the bugs climb into my spring onions, I would have thought they don't like spring onions.
The cabbage >> greens thing was quite annoying, they shouldn't be selling you some other seeds, that's quite dangerous and unprofessional. Have to make sure I buy my seeds from a reputable source in future