While I think DHS needs work, I think it's unfair to call it less than a half day park or only good enough to have dinner.
It still has Tower of Terror which is incredibly well done and by any reasonable measure, a true E-Ticket. It's a top 5 attraction ever at Disney and possibly anywhere. It represents what I wish Disney still aspired to be.
RNR is one of the smoothest, most fun roller coasters I've experienced. It's well themed and a good mix of thrill and fun.
Great Movie Ride is classic Disney, admittedly in need of refurbishment, but not missable.
Fantasmic is a must see show, despite its age.
Toy Story is good old fun and can't be missed.
Mix in some food, Star Tours, Little Mermaid, and Beauty and the Beast stage show, and I think you've got a reasonable amount to do. I do acknowledge The Backlot Tour was a travesty and Lights Motors Action is old and tired. Refreshing it would be refreshing.
Anyone can argue Beauty and the Beast or Little Mermaid are old and tired, but they are classic and how many attractions across WDW can you say are in need of attention? That's the bigger problem for me. I could say EPCOT is a half day park too if I really want to get picky....everything there is old.
And I know you can do what I listed at DHS in a half day if you hustle, but I'd argue that you aren't a Disney fan if you can either miss things I mentioned or rush through the park that quickly. I've done all of MK, literally every attraction and show in less than 1 day. Does that mean even MK is a one day park? It depends on crowd level, your level of interest, and how long you spend enjoying the details of Disney.
I think DHS needs more to do and serious updating, but I can make that argument for AK and especially EPCOT. However, calling it a half day park just means you're skipping things that don't interest you anymore (maybe for good reason) but that argument can be made for any park.