All screenshots are taken with the world's time frozen at noon, and the game's brightness setting at "moody'.

In 1.16.5, during the day when the sunlight is at its brightest, placing a torch had an almost imperceptible effect on the visual brightness of surrounding blocks.

In 1.17, you can see the light from the torch much more clearly, even with maximum sunlight. This is because the visual brightness given by sunlight has been reduced. Compare the top left image to the bottom left image, and you'll see that the grass is darker on the bottom. So the torch did not get brighter, the sun got darker.

I'm submitting this as a bug because I do not see anything in the 1.17 patch notes that indicate it was intended.