This is an apple's to oranges comparison. Lambda-CDM is a theory of all cosmology, including galaxy formation. The dark-matterless galaxies are a problem for Lambda CDM because they don't easily fall out of numerical simulation during formation. Supermassive black hole mergers also don't fall out of numerical simulation easily, but we still observe them.
They're not a problem for the concept of dark matter in general, since they have good agreement with the idea that the phenomenon creating dark matter appears to be a massive particle of some sort capable of being spatially dislocated from visible mass. So a theory proposing a pervasive but ill-described massive, mostly non-interacting particle may just be under-explored or the ramifications of the full scope of possible dark matter configurations (as pure mass) not explored.
It is a problem for MOND, which proposes that all matter is generating this effect which looks like dark matter (and then has an extremely poor ability to explain the rest of cosmology or work within the framework of general relativity).
They're not a problem for the concept of dark matter in general, since they have good agreement with the idea that the phenomenon creating dark matter appears to be a massive particle of some sort capable of being spatially dislocated from visible mass. So a theory proposing a pervasive but ill-described massive, mostly non-interacting particle may just be under-explored or the ramifications of the full scope of possible dark matter configurations (as pure mass) not explored.
It is a problem for MOND, which proposes that all matter is generating this effect which looks like dark matter (and then has an extremely poor ability to explain the rest of cosmology or work within the framework of general relativity).