The fact is, in most cases you will probably multiclass your rogue to beef up its combat ability, because, well to be honest - no it doesn't scale that well at higher levels. There are lots of options for doing this, most involve Barbarian, but sometimes fighter.
Having said that - the advantages stealth characters have makes sense to me in this context because if you can't sneak attack every round your dps is going to be terrible compared to other classes UNLESS they give you the ability to make different kinds of poisons that are progressively stronger, or sneak attack with the special arrows you find in game.
Basic poison is 1d4 but Wyvern poison is 7D6 - uh...can we manufacture that or other poisons like it? But then, other classes could just use it as well.
