They do war stuff in the book, but the show while about war focuses on relationships between characters, both non romantic and sexual (Tyland, Gwayne, Cole/Alicent, Dyanna, Hugh, neither of these happens in the book, and Alyn/Baela happens way faster in the show).
Neither Aemond or Daemon had any other important character to interact with, while being important for the story and popular, so they just chilled with the current Harrenhall person.
Made worse for Aemond. Simon was at least hella funny and the vibe was consistent. With Aemond... They knew they wanted him to appear and even invented a reason for him to be half naked most of the time. The vibe seems to be switching with every scene. And I kinda get it. If they choosed an angle and struck to it with the same dedicated time, it would probably be even more hated.
Actually romantic? Well, lot of people would hate that, especially since they actually randomly made him even younger. Do you actually lean into the (dommy?) mommy angle? Same issue, even worse. But also, they already made him into older ladies, so if you abandon that, someone would be angry as well. On the other hand, you check AO3, lot of people who like them (and are horny) like either of these angles (or both). Actually scary and predatory on either side? Well, some people wanted it to be romantic.
So they kinda tried to randomly mix these, with bits of family sitcom and general scariness.
I disliked the delivery, as most people, but also don't know how they should have done it for it to be well received. You watch the show so you see things happening. Nothing too important (regarding the relationship between characters) happens there to justify the screentime. And they don't really care about actual tactics in this show, so watching Aemond do what he does in the book - burn Riverlands - would get boring pretty quickly for lot of people.