I like the new dialog? I basically always crop the image when screenshotting so the new UI results in less button pressing for me. How often do you need to capture your entire screen? I almost always want to focus on something.

There was already a way to do that. Cmd-Shift-4, drag a rectangle around what you want to screencap. Cmd-Shift-4 Space, click a window to screencap it.

These have been in the OS for so long I can't even remember when they were added.

https://support.apple.com/en-us/102646

I usually want to capture a window, not an arbitrary region (and will sometimes resize a window before a screenshot to enable this). Hotkeys already supported this without cropping needed, and with bonus proper transparent corners.