One of the reasons I suggested building these circuits instead of 'armchair analysis',
is that computer simulations are often way off,
or lack key elements of actual functions in a real-world circuit.
Bob Pease, (Troubleshooting Analog Circuits) the man who invented Op Amps,
had the same important advice to all theorists
and especially grads who tended to rely on computer simulations:
Build it. Test it. Find out what it really is doing,
and then re-examine the whole thing.
Don't rely on calculations, or especially computer simulations.