I mean given that we see the Twins are actually incompetent and Andras would have self destructed the army and Jezera would have scared off all allies, I am not so sure.
The Twins have character flaws that make them somewhat incompetent at some of their functions as rulers, but they also have their talents as well as pretty powerful magic. More importantly though is to keep in mind that their opposition so far has been just as incompetent as them, if not more.
I haven't played the game in a long while and I'm not familiar with all of the recent changes, also I forget some names so forgive me on that, but lets breakdown Rowan's contributions:
Taking Raeve's keep - that was just a test for Rowan, the Twins alone could have taken the keep if they wanted to but they wanted to see if Rowan was capable.
Creating a network of supporting villages and mines - they probably wouldn't have been able to do this as smoothly without Rowan, but the importance of those is more to create a supply network for the future, as of conquering Rastedel this asset has not been critical yet.
Recruiting the local orc army - Rowan was helpful in doing this, but realistically the leadership of the orc army was already unstable. Even in the scenario where Rowan frees Delane and doesn't make any alliances for the Twins, Tarish gets rid of the other 2 orc warlords and then makes an alliance with Andras to consolidate her own leadership. Maybe the timing of everything wouldn't have worked as perfectly without Rowan, but worst case scenario Andras just bashes enough heads until Tarish or another warlord is willing to bend the knee. Would have wasted some warriors but would have worked nonetheless.
Defeating the Rastedel army sent to check up on Raeve's keep - Probably Rowan's greatest contribution, he came up with the winning strategy and made sure the battle was won without word of it getting back to Rastedel. Twins could perhaps have won it without his assistance, but without as clean of a result and could have exposed the Bloodmeen army to the world.
Conquering Rastedel - Once again, while Rowan made perfect use of the situation to destabilize Rastedel, all of the pieces were already in play. The shapeshifter ally was already working for Jezera in there, tensions between the purples and the coppers were already near their boiling point, the relationship between the baron and the priestess already existed, etc. Again, without Rowan's assistance in defeating the army, maybe Rastedel hastily puts together more of an united front in face of the demons, but there would have still been a lot of instability and dissension among the ranks. Without Rowan the demons don't get Rastedel delivered to them in a silver plate, but I think they could have still won it even if they had to fight for it.
Now make no mistake, Rowan's contributions put the demons in a MUCH stronger position by the end of act 1 than they would have been without him. But even if they would have been much more bloodied and in all likelyhood their aspirations of world domination would go no further than Rastedel, I do think they would have still managed to accomplish all of their act 1 goals, just in a much more messy fashion, for better and worse. In that sense I think Rowan can still justify his actions in act 1 as being the "least damaging" course of action, but smoothening things too much might be slowly turning the Twins into too big of a snowball, and if he can't oppose their sadistic whims going into act 2, then he will have created a much bigger evil than the ones he sought to avert.