A couple thoughts on this topic, obviously nothing comprehensive. For frame of reference, I did three tours in Iraq, including with 4th ID in 2003.
Logistics: If the Saudis cut us off, we'd be screwed. Bullets don't magically comes from nowhere. Nowdays, all the support comes in through Kuwait, which makes us immune to the vicissitudes of those Saudi scum. The Kuwaitis know which side their bread is buttered on. But in 1991, Kuwait City harbor was not quite in shape to handle 500K worth of troops. So any POD MUST take into account how Geo. Bush Sr. bullies the Saudis into signing off.
Iraq's ability to sustain an insurgency: Much, much reduced from where it was in 2003. Hussein had spent 13 years stockpiling weapons and ammunition and hiding it out in the desert. 9 months after we got in, we were still finding ammunition supply points out in the middle of BFE nowwhere in the desert. Most of Iraq's weapons and ammo were burning in the middle of the desert in 1990.
Leadership: In 2003, much of the Ba'ath leadership fled into Syria, where it formed the initial core of the "Former Regime Elements" Sunni insurgency, and created the logistical support structure that kept the Sunni insurgency alive. Not going to happen in 1990, because they never believed that regime change was going to happen. In 2003, they believed. We were supposed to prevent that (secondary objective for 4ID was sealing the Syrian border) but the goddamn Turks stabbed us in the back.
Other players: No AQI. This is a major deal.
Iran: Damn good question whether Bush I could have handled them better, or whether they would have gotten as heavily involved in a proxy war with the US. My theory is that, just as in OTL, within six months we'd be catching Qods Force in Iraq. Which means the Shia insurgency works out the same or worse.
Took us pretty much 7 years to end the insurgency in Iraq (yes, this is what Iraq looks like in a time of relative peace -- compare to number of Iraqis killed by Iraqis during the Hussein era), but a lot of that has to do with variables that aren't quantifiable, and that most people don't understand well enough to try to quantify. Shoot, if my POD was CPT Travis Patriquin dying in a training accident in late 2005, it might add a year to the insurgency's life. It might not matter in that someone else would hit upon the same idea. (CPT P. invented the Sons of Iraq, which basically ended the Sunni insurgency).