Unfortunately, Lynn Royce probably had a terrible childhood herself no role model of what good parenting looks like. Cycle of abuse/neglect continues.
I think what was well done at the end of Happy Valley was that they didn't go down the road of an unrealistic realisation by Tommy of what he had done wrong himself - he was likely incapable of that for various reasons, not least that having been left to his own devices since being a tot he would have decided he knew best at all times (with nobody to tell him different). So he wasn't suddenly going to see everything he had done wrong personally, the introspection wouldn't have been there.
But - whereas Catherine maintained that Tommy was only getting to know Ryan to get back at her, it did seem that Tommy had found some sort of heart buried inside him. He recognised the good life that Ryan had been given by Catherine, and instead of being resentful or jealous because he didn't have that himself, he acted for perhaps the first time like an actual dad, putting Ryan first not his own feelings, and expressed (in TLR way, which naturally is twisted) gratitude. It was good.