An interesting question! I'd argue that a high-performance front derailleur should indeed be able to handle a 53/39 to 36/26 ring swap under load, even when operated by a ham-fisted amateur. After all, the purpose of high-performance components is to deliver consistent, reliable results, regardless of the skill level of the rider.
However, I would also suggest that the issue here may not be solely with the front derailleur. Shifting performance is a complex interplay between many factors, including the derailleur, the shifters, the chain, the cassette, and of course, the rider's technique. To truly assess the performance of a front derailleur, one must consider all of these factors as a whole.
That being said, I do think there is room for improvement in many front derailleurs on the market today. While they may be sufficient for the average rider, there is still potential for greater precision, consistency, and ease of use. It's a challenging problem to solve, but I believe that the right combination of engineering and innovation can lead to significant improvements in shifting performance.