Why is burst/automatic fire bad for suppression when the weapon designed primarily for suppression(i.e. MG) is used almost entirely in full auto?
Depends entirely on your standards which are primarily subjective. For modern military doctrines usually 22lr after going through some arbitrary amount of armor(usually some unspecified steel) is ok. Do you want to incapacitate the man immediately? Do you want to wound the man enough that his life is in danger and requires immediate medical help? Do you want to theoretically be able to kill your target on occasional lucky shot to the eye while other shots in non-vital areas like ones not being arteries/heart/nerve system are expected to only cause minor distraction for the expected time of combat?
Hunters have more strict standards as they can lose the game and/or talk some weird speak about muh ethics, though they don't really have standards for humans, for obvious reasons. For deer the lowest acceptable cartridges for a standard lung shot are 357mag(1250ft-lbs) or 30 carbine(~1000ft-lbs, commonly more like 950) from rifles, though handgun hunters might have it lower. These standards are for pretty close range(50-100m) though, and with a properly selected ammo. Humans are generally considered similar or slightly smaller than deer sized game and when fighting them you may find it acceptable to take 5mins to bleed out instead of >30secs or instant incapacitation and when they fight back you can simply shoot them again so the acceptable threshold can be lower. Usually if you can get good ammo then energy is a pretty good estimation of "killing power" and the one that legislations that don't list specific cartridges commonly use.
For elk do your own research, i dunno.