I tested rogues quite extensively in version 392. I haven't played 435 yet, and I know some significant things have changed, so any of my observations may no longer be accurate. Based on my testing though, rogues were amazing. I was able to clear Path of the Damned quite easily with a party of six rogues. Backstab does a heap of damage. Although, at least in 392, you could not Backstab with an ability (such as Blinding Strike). It had to be just a normal attack. If you used an ability, you didn't get Backstab damage. You COULD do it with a ranged weapon, and didn't have to be right next to the target, but still pretty close. Backstabs with arquebuses or blunderbusses (especially Lead Spitter) could be quite spectacular. Even without Shadowing Beyond, you could have one Backstab every encounter, and more or less kill or nearly kill a target right in the beginning of a fight. Sneaking your rogue back to the rear and gibbing an enemy spellcaster at the start of combat is pretty great.
Shadowing Beyond is much more powerful than I think people are giving it credit for. I'd go so far as to say it's the single most powerful talent in the game. It's the only thing (that I know of) in the game that actually lets you leave combat/reset combat/escape. This is super good for, say soloing (especially soloing PotD or even Hard). It lets you do things that you cannot do without a rogue who has this ability. Did you know that if you have at least one rogue, you can complete every quest in the backer beta (and level to the beta cap) without killing a single thing? You can ALMOST do this without a rogue (just decent stealth for your whole party), but not quite. Because there's no way to get into the temple of Skaen without triggering a fight. Either against the beetles around the statue entrance, or the leatherworker and his apprentice in the shop. But if you have a rogue, you can sneak up to the statue and initiate the scripted interaction, open the way to the other map, then when you are automatically popped out of stealth and attacked, you can use Shadowing Beyond to exit the encounter. Then you can just sneak your whole party up and hit the map transition before you're detected. You can also do things like get the dragon egg without having to fight or pay the band of mercenaries, by doing the same thing. Sneak up, do the scripted interaction, get pulled into the conversation automatically, but then just Shadowing Beyond your way out of it. If you really want to cheese things, (or you're soloing a high difficulty), you can just sneak up, assassinate a single foe quickly, then vanish with Shadowing Beyond. Repeat as often as you desire, resting every couple of times. You can clear whole maps full of grouped enemies this way. Which can only be done with Shadowing Beyond. Any other class would have to kill all of the enemies of a group once they became aggro'ed, unable to leave the map until they were all dead. But the rogue can hit and run, unlike anyone else.
The all-rogue party (or solo rogue) also has the singular ability to duck out of those annoying situations where you get forced into a cutscene/dialogue and then jumped without having the chance to position or open the fight your own way. When that happens, you can just have everyone Shadowing Beyond, and then you can leave or use your stealth opening on the enemies however you wish.
Now, maybe there will be other means of gaining in-combat invisibility which drops you out of combat. Like invisibility potions or something. If so, then Shadowing Beyond is much less cool. But if it remains the only way to actually leave combat, it will have enormous utility in many ways throughout the game, most especially when soloing, or doing trial of iron + path of the damned. Being able to complete more quests without having to fight will let you level up more before having to fight. Not for my first playthrough of course, but after that I'd like to run a solo rogue and find out exactly how high a level I can get in the whole game without having to kill anything.
Maybe this has all changed in 435 or later versions. I dunno. But calling Shadowing Beyond useless is just plain unimaginative. And Backstab is quite good as well, if you use the right tactics. Of course, some people don't like stealthy, deliberate, planning-intensive roguey gameplay style. In which case, yeah, it's a lot less good. But I think it's amazing.