Well, from my / mates experience they are, but only when in fairly constant / normal operating scenarios (10:1 - 17:1) PULP, piston motor accelerating.
But your correct other factors like super rich / lean, big cams, decel, ignition misses, too retarded ignition can make things very uncomparable Iv seen super retarded ignition increase EGT's instead of lowering Ie.
Thermocouple per cyl and a decent A-D box is just so much cheaper then 6 LC1's. If only we could warrant the cash :\