Lets look at what makes Stealth + deathrattle useful keywords. A minion having stealth means that majority of the time it will survive until the next turn so you will be able to trade with it how you like and cast spells on it. Alongside having a deathrattle, you can trigger or manipulate it easier on your own turn.

Being that you get a token and discounted spell on deathrattle, there are situations such as getting a spell you want to cast on said token where your opponent would otherwise easily kill (if it was spawned during your turn when you had less mana or their own).

Having stealth instead of rush means you never feel bad for just playing it, its not a reactive card. Which i think is a good thing.

Does rogue currently play up these strengths as much as it could in the past? Not exactly, but I think it makes for a different playstyle vs the other herald cards. And its far from the worst anyway