I have noticed deep and powerful transformation as a result of EMDR and IFS (Internal Family Systems) therapy. Both can rely heavily on language around visualization for sure. I have assumed for most of my life that that language was metaphorical, and have always translated what I "see" internally based on what I know/feel/hear/smell/taste instead. I would say having a therapist who is aware of, and sensitive to aphantasia could lead to a better experience. For me, what I noticed most throughout EMDR is a change in how my body feels more than anything. As I moved through the treatment I noticed changes in the embodied experience of recalling traumatic memory. At first I felt a lot of nervous system activation, and by the end I almost felt joyful recalling the memory. For those who have less interoception happening than I do, or less awareness of their personal style of "knowing", I could see EMDR feeling like a waste of time.