Again, no bummer energy intended...
1. I never said *all* steel frames last longer - because a poorly brazed steel frame wouldn't - but I did say steel frames last longer ~ because they do.
As a material under load steel and in general (after all there is a reason steel is used in, say, skyscrapers and not carbon) will outlast carbon as carbon degrades not only under UV light but significantly under, what would best be categorized as incidental stresses ~~ road debris dings/chips/dents/etc. Steel, for the most part, is unaffected by this.
And yes, while carbon is repairable - some carbon not all - all steel is repairable... and as most people in the bike biz (or biz of bike) would say, "Do you really want your plastic frame repaired, in particular something as critical as the fork, or do you want it replaced?"
Finally: fatigue... I'll assume you know how brutal a carbon failure is versus the "heads up" warning signs of steel.
2. Outside of weight savings and tech I personally have met no cyclist who, if they have nothing beyond experience and honesty invested in the statement (ie: nothing to gain or lose by saying it), hasn't said or admitted that carbon pales to steel in comfort. Comfort meaning ~ flex, torsion, planing, "kick" at the rear triangle through the bottom bracket when pedaling hard out of the saddle while climbing.
For a racing cyclist, just like in F1, carbon makes a lot of sense for the weight savings. It makes even greater sense if the person doing that racing is sponsored.