Bertie the Bunyip writes:

You gotta have some good old fashioned stuff for backup..

Well, until recently you did anyway!

I fear what may happen when there is no longer a back-up--or when pilots
forget how to use the back-ups.

Also, while you may have some back-up instruments, a situation that would be
both safe and manageable with a complete avionics suite in working order can
become dangerous and unrecoverable if you have only a handful of instruments.
There are some things that you can do with fancy avionics that you cannot do
with just two or three steam gauges ... otherwise there'd be little point in
the fancy avionics. But this inevitably means that there will be situations
that are safe with the fancy stuff that become deadly without it, even with
back-up instruments.

Flying with three or four instruments is fine as long as you limit your flying
to situations that can be handled by those instruments. Of course, if you
have a fancy glass cockpit, you may well go far beyond those situations, and
if the glass cockpit then fails, you're in deep trouble.