Amiable had a stronger meaning at the time. It’s a very mild term now, meaning friendly, agreeable, easy to get along with, nice to have around. It used to have stronger, deeper, positive connotations of being good and admirable.

Similarly, ‘mischief’ had a worse connotation then than it does nowadays, when it practically suggests ‘harmless’.

Yes. I was 18 when Harry Potter first started getting notice (before the 4th book came out, or the first film.) I wished I’d had them as a child.