It really depends on the lettuce.

Iceburg seems to be intentionally useless. Romaine starts to have a little flavor. Leaf lettuces have a wide range of flavors.

Moving to California recalibrated my understanding of lettuce/salad greens. Not sure if you meant just lettuce, but in California a typical salad has little to no lettuce, and instead: mizuna, arugula, radicchio. What lettuce is does have is Romaine and butter lettuce, not iceberg.

The result is a very flavorful salad- intensely bitter with much less crunch.

is that the outcome of nature or selective breeding?