I happen to be one of the folk who say 'if only he had a spine', which is a pretty easy position since just about every one says it.
but, if he had a spine, it's highly likely he creates a civil war. add in some intelligence to the spine, it becomes a different story, but that is never added into the equation. It's always a case of 'what if he had a spine and chose one side or the other'. Let's not get greedy in reinventing his character.
He invited his demise by summoning the estates general. He could possibly have imposed his will with some political savvy before that. After that, though, he has to outright dominate one side by siding with the other. that's recipe for civil strife. He tried going this way and that to avoid it, and ended up losing his head.
So, if he decides to grant a constitution, the opposition forces have full ammo to attack him with and weaken his regime. Does he have enough to withstand the onslaught? Will the moderates back him if he doesn't become their toady? = the conservatives are going to be his enemies. The moderates will be fair weather friends. But if he goes the other route, the conservative will be the fair weather friends unwilling to give an inch, and the moderates will be his enemies.
the time to take a stance is BEFORE he gave every one a seat at the bargaining table. afterward, he's going to be a figurehead, so pick a side and hope it wins. Beforehand, he can shape events.
For him, personally, any course of action is better than the one he took, or at least can be no worse. For the country, it's debatable. I think the country was ripe to explode and would have required a lot to keep it together. Maybe the reign of terror, where blood ran freely, could have been avoided, but would the alternative have been much better? that kind of depravity isn't a fluke of circumstance. It's part of a societal core. Maybe it would have been bottled up, but I think it would have been easy to unleash in some form, so I don't believe in the notion that 'if only he had done this it could have all been avoided'.