I think all the other Spares, who have been booted out of dysfunctional families, where the slightly boring heir is Lionised, might feel some sympathy for Harry.
I know, move on, but he did have a lot of childhood trauma, there was empathy for him. The whole system is trauma inducing. Other victims of unfairness and trauma possibly are in his fan base. (yes I know William also suffered trauma, and sought out treatment and healing, perhaps dealt with it better, but William always knew he would be King, his life path was more secure. Harry always knew he would be edged out, despite being part of the dynamic duo).