Casual players are not generally very keen on 50+ hour RPGs.

If a game has an ending it can't be an RPG? You are certainly entitled to your opinion and choice of games, but I don't think you know what an RPG is. Neither Diablo or WoW invented the RPG, and while respawning is certainly possible in an RPG, it is absolutely not a requirement.

Right now you can play the game for 50+ hours, explore everywhere, get to level 35 and finish the game... and that's crap. However, get rid of the ending, and respawn monsters so you can fight them over and over for two years until you reach level 999, and that would be an RPG?

Regarding your earlier comment about the game 'limiting' you to moving forward to progress, there are quests to do and places to explore. You are not bound to a railroad track style gameplay if you can not kill the same opponents over and over.