How can I deal with low-key plagiarism?
I agree with your assessment that this is misleading behavior on the part of the authors. I have run into this kind of behavior myself, including from authors who were famous researchers (and who were famous because they actually did very good work and not because they were good at misleading people about doing good work). It seems like it’s just human nature for some people to feel a need (probably driven by insecurity and lack of self-worth) to play up their own greatness and belittle others’ achievements.
As for what to do, I’d say just keep publishing good work and don’t worry about it. It’s not worth the time and energy it would take to fight such petty misconduct, especially when there is no hard evidence for a dishonest motive. Moreover, the advantage that these authors derive from such underhanded behavior probably does not outweigh the disadvantage of other people looking down on them and not wanting to work with them (I’m willing to bet you’re not the only one who noticed this), so their behavior is self-defeating and self-punishing. And your own contributions are documented in the scientific literature, so in case a dispute ever arises over something important, the truth will will be easy to establish and will come out.