Sounds like you need a large dose of git gud, mate.
More than once I've run over a Stank because the idiot believes he is completely invisible, they do show if they are close enough to you, the thing is that when you drive a mammoth your attention is everywhere but on your surroundings, hence why they can barely see the god damn air strikes incoming most of the time.
And regarding SBH, it just sounds like you are shit at spotting their ass, most of the time is the same deal with STanks, the average SBH thinks he is hot shit and tries to go past you, more than once I've killed or spot one becaues they think they can go in circles around me, bunch of fags.