Carbon fibre is stronger than steel of the same weight if it is used as part of a structure
So a tube of CF will bear more weight than a steel tube
Carbon fibre bike frames are made as "one part" there are no joins. Usually, steel (or Ti or Al) bike frames are made from tubing and have weak points at the welds. Some forks are made from a metal steerer column and carbon fork legs. Failures at the join are common enough for most people to advise avoiding this construction
Those are the two points in favour of carbon strength. Carbon has other plusses, such as directional compliance - when it will bend in one plane but not in another
As for the against, CF on bike frames is not as abrasion resistant as steel frames. What I mean by this is that if you rub on a carbon frame in one place it will cause damage to the surface. The same is true of the paint on a steel frame of course. However, the abrasion on a CF frame will continue through the layers of material and could result in a hole. This happened to me recently and I had to repair a CF frame. See my blog for details
https://audaxing.wordpress.com/2019/09/07/carbon-fibre-repair/
Another related problem is that in some circumstances, it will make a weak spot or "stress point" which is prone to act as a fault line for cracks. This happened to me during LEL 2017, my CF seat post snapped at the seat collar due to wear.