For repetitive production welding it is so, and I would defy any welder to put down a bead like I see CNC welder do on fine edge aircraft heli-arc for ten thousand times in a row.
Now, if you want to send a robot to do a one time only job, then you are correct. Like this whole conversation, this is about production based and repetitive predictable motion. Just try cutting your lawn exactly the same path every week, never mind cutting the lines exactly straight to say 5 thousands of an inch.
Robots are probably better in any situation where the work can be jigged, fitted, and aligned perfectly every time. That's practical on small scale, high production pieces. It gets harder to accomplish and justify the cost as the size of the assembly scales up, and/or production numbers scale down.