The witcher and tes are very different games, i still have no idea why people are always comparing them. I do think that bethesda has stepped up their writing with fallout 4, and i personally hope they adapt alot of what they've done with it for the next tes. Settlement building, a political main quest, less derpy lines and better dialogue over all. Morrowind and oblivion really didn't have any dialogue, and skyrim made the dragonborn out to be a bland idiot. I'm hoping they add in more reactivity to the world, maybe make the races, guilds, and main quest have an impact on what is going on in the game.
Also i'm still playing fallout 4 fairly reguarly, (thanks to the dlc, radiant quests, and settlement building) i haven't touched the witcher since i beat it, i also don't plan on getting the dlc for it. I think making your game too dependent on story makes it loose replayability. Having content to keep you busy (even if it is just lame radiant quests) is something that the witcher devs could learn from imo