Well it doesn't have to be weak like that. It's not like "meow, neverminddd" and then he slumps away. There could be some alternatives. For instance it can be very dramatic when a super villain, right when he is about to do something, instead kills himself. Or, he raises his hand to push that final button, or raises the weapon to slay someone at his mercy, only to drop the weapon at the last minute. If done right with enough suspense, it can be very dramatic. ie Russell Crowe in Gladiator (not a villain but a force of ruthlessness nonetheless in this particular scene) sparing the life of one of his biggest opponents, while Caesar sits amused and the crowd boos him with disappointment . Imagine some elves and other Elvehn are outwardly disgusted and angry with Solas for suddenly changing his mind at a critical juncture, and then you have a massive battle alongside Solas against all the elves and Elvehn.
I would honestly love to see this kind of scenario for Solas. As much as he talks of his plans, I still have a hard time believing that, when push comes to shove, he'll actually do it in that critical moment. He's already responsible, in his mind, for untold suffering. Will he really cause more? Before Inquisition, I think the answer was a simple yes. Before Inquisition, modern Thedas was barely real in his eyes. But not now. I think he's already been too exposed to the current world and its people to destroy them all. He's posturing, he's got himself convinced he'll do it, but I'd like to think that, in the end, he won't be able to push the button.
But I am a "hope for the best, prepare for the worst" kinda gal, as is my Lavellan, so I'll still have to be ready to persuade or stab him if need be. lol
On topic, I found reviewing Solas' comments after having completed the game more interesting than examining Anders' b/c, like others have said, Solas is actually hiding something the whole time. There are a lot more aha! moments and extra shades of meaning for him than for Anders once events happen. Anders you basically have to wait till Act 3 or so to start getting that.