Yeah I think it's pretty underappreciated how Harimoto's game has developed, especially since his style is basically unique among the top tiers of men's players at the moment.
Your post made me think of an interesting cross-sport comparison for Harimoto: Andy Murray (now retired, but I'll describe both in the present tense). They were both hyped juniors who play(ed) a counter-punching/placement /pace variation game rather than all-out power, despite having efficient and powerful strokes off of both wings. Their tendency to play passively occasionally gets them into trouble against lower-ranked opponents that they should be expected to beat easily, but they also consistently challenge the (other) top players. Early in Murray's career, many wondered whether he had peaked, and doubted that he would ever be able to break through against the big three and win a slam, etc. But he gradually added more dimensions and aggressiveness to his game and eventually achieved the number 1 ranking, won three grand slams and two Olympics gold medals in his career. Ofc it's impossible to say whether Harimoto will be able to reach comparable heights, but his recent improvements are some sign he might be on that path.