I am always disappointed when people paint any martial practice with a broad brush. The ability of each person to transfer lessons from bokken to katana is decided by their interest, innate ability and the quality of instruction. Within a single school the experience of students vary widely. At Aikikai of Philadelphia for example, I was introduced to Henry Smith Shihan (Chiba/Sugano weapons), Nizam Godan (Nishio/Seito weapons) and Paul Manogue Yondan Aikido (Yagyu Iaido master plus a bunch of other weapons training including Shioda Shihan) all in my first two days. In the intervening years I have studied with Gleason Sensei(Saotome influenced), John Stevens (Shabata), Dwight Epps (Crane Iwama interpretation) et al. My "aiki weapons" is unlike any of the other students in my school as well as unique from each of the schools that have seasoned my continuing study. The rambling point that I humbly submit is that we are best served to actively pursue whatever level of expertise we choose and abandon all judging of the illusory/intellectual merits of various weapons styles. The goal is always self mastery. Aiki weapons is a beautifully wide and flexible path.
Over the years I have practiced with a lot of Aikiken people, and a few koryu people, both in kata and in sparring. I have often presumed to be annoyed by a going-through-the-motions quality that is all too typical of Aikiken practitioners, and likewise presumed to be annoyed by a -we're-the-real-deal-because-we-have-a-lineage attitude of some koryu people. But broad brush strokes are a disservice to the truly talented people who can be found in Aikiken and in koryu.
To get back to the original question, I would urge the student to visit potential teachers, do some research, and do some thinking, before deciding what and where to study, just as for any other aspect of martial training. To dismiss Aiki weapons training would be to dismiss, for instance, Ledyard Sensei, who practices some very powerful stuff indeed. And to prefer koryu because, well, because it is koryu, might be to embrace a vitiated echo of a once vital art.