The VSI only lags in giving a RATE of climb/descent. In smooth air, or
smooth pilot inputs, the VSI will give nearly immediate response up or
down.
I could live without the VSI, or the AI, or DG, and make do with the
rest of them and do a decent approach. I began teaching what I call
"Primitive Panel" over 30 years ago with a loss of gyros, then taking
away the Turn/Slip, the VSI, and leaving the student with little to
work with. They can do fine if they use their heads. Too many times in
over a thousand hours of actual IFR I've seen gyros fail as well as
other instruments and you had to extrapolate all the available
information. So far so good......
Ol Shy & Bashful