I definitely think that Tommy idealises Grace because she died, and I always thought it’s weird he only hallucinates her when she was just “the barmaid” and not his actual wife.
Tbh I don’t think their marriage would have lasted if she hadn’t died young, because they never really knew each other in the first place. Their relationship was based on them projecting on each other. Tommy didn’t see Grace for what she was (a snitch from the Parrish) because he was blinded by his infatuation with her and saw her as an escape from the War, saying he “can’t hear the shovels” when she’s in bed with him. Meanwhile Grace continued to spy on Tommy despite her “love” for him and only admitted to what she’d done at the last second and fled Birmingham before she could be made to face any actual consequences, then expected him to flee with her and abandon his home, family, business and gang all for the woman who betrayed him. The fact she seems to genuinely believe he would have done that and blames the fact he didn’t on why their relationship didn’t work shows that Grace was always extremely entitled when it came to Tommy. (She also pushes the blame on him when she gets pregnant “the fault wasn’t mine”. She pulls the “I love you” card when it seems like she might lose him to May or Lizzie.)
Polly even explicitly tells Grace to her face at her wedding that while Tommy has chosen to conveniently ignore all the shit she did to him, but that doesn’t mean the family has and they only place nice for Tommy’s sake (and possibly the baby). It makes sense that Tommy thinks of Grace as her pre-betrayal incarnation, when she was someone he thought could be trusted. He still conducts gang-related activity under her nose at the wedding and even two years, she’s still pestering him to tell her what he’s really thinking.
So yeah, I agree.