Of course, as far as the 139 is concerned, if you have EGPWS, it will clearly show you where you can and cannot go with respect to terrain and if you are flying on autopilot, the autopilot will avoid terrain showing on the EGPWS.
Part of the acceptance flight test where I worked was to fly towards a hill with ALT HOLD enabled, at an altitude of 2-300 ft lower than the top of the hill. When EGPWS starts to freak out, autopilot initiates a climb up and over the terrain.
Synthetic vision is available on the Primus Epic system used in the 139 (Honeywell have a 139 themselves and it has it installed), but, if they go ahead and certify it, it would be a HUGE expense to operators to have it installed on their machines. Welcome to Honeywell.
Hence the 169/189 have a different avionic system installed!