I'm not an expert, but if that's an exterior or load bearing wall, it might have been better to drill holes for the drain line instead of lopping off the 2x4s. You may want to consider putting in some sister studs to return the load carrying capacity. Those "braces" aren't accomplishing much.

"Those "braces" aren't accomplishing much."

They protect the pipe from drywall screws, nothing structural about them.

I'm not sure if you're a contrarian or something else. I'll give you the benefit of the doubt once again.

Your comment is inane. The pipe appears to be set back far enough to be safe from normal drywall screws. But say someone used too-long screws, just what do you think having that wood there accomplishes? If the screw is long enough to hit the pipe, it'll hit the pipe. But the screws will oc of the 2x4s and not hit the "braces" anyway.

That notching is not as bad as you all imagine. That is a 2x6 or maybe 2x8 wet wall.

Does one ever need to raise the plumbing because of a new sink? I've always had plumbers simply connect the "water in" pipes to the faucet w/ that flexible pipe, and the drain simply gets an extender to go down to wherever the drain itself is mounted on the wall. Sometimes even sideways!

It's actually pretty simple; I've had 4 sinks replaced, and that's what they did in every case.