This is true and, to be honest, I think it became more of a tourist attraction, than a place for anyone local (ish) to actually go shopping there and, for the most part, the service was appalling, so it’s not surprising that shops moved away (the rents and rates much be astronomical). I bought a Gretsch from Anthony Macari back in the day; it was always a strange shop.
I remember when it was called the Fender Soundhouse and they were in Tottenham Court Road, in my memory, it was massive. Rose Morris were in Shaftesbury Avenue (saw Rory Gallagher in there once) before they moved to Denmark Street. Thinking about it, the area was a good place to see guitar celebrities: I saw Laurie Wisefield window shopping outside Macaris and Hank Marvin in Argent’s.