There are four non-shitmons that stand up to Psychic+Shadow Ball; Melmetal, Mega Gyarados, Chansey, and Alolan Muk. Mega Gyarados gets 2HKOed by Dazzling Gleam, so if the Alakazam user predicts your switch Gyarados dies. Neither Pursuit nor Assault Vest exists, so Alolan Muk does little outside of switching into Alakazam.
That leaves Melmetal and Chansey as the only consistent, broadly useful switch-ins. Even then, the lack of Leftovers/Eviolite means wearing those two down with attacks and Stealth Rock for a Calm Mind sweep later is a very real possibility.
