I heard you the first time, a deer walking on a timbered ridge at 400 yards
No, you didn't hear me the first time.
If that deer is walking, there's no shot.
Plenty of time to range and dial though, and WAIT for a shot.
You act like you don't see many deer, and have to "hurry". Around here there's always another deer, and another opportunity. Let the sketchy shots walk.
You're defending haphazard holdovers and I'm saying buy an optic appropriate for the job and learn how to use it. Just the simple body size of the deer changes your point of impact because your references are different from one body size to the next, and can lead to an effed up shot. Learn something about ranging with a reticle and subtending target size, and you'll understand what you're being told.