I challenge you to find a c biased guitar amp with a cathode resistor per valve and moreover one without a decoupling cap!
Regulated bias? Waste of time since the time honoured method compensates well enough for HT variations.
Cheap resistor network? Do you mean a cap and R off the HT winding? Yes some "famous" names did that and "we" paid for the results!
Low Z? How low do you mean?
PI to op valves is almost universally 100k anode load, 22nF ish and 220k grid leaks. The A100 is like this (but a proper bias winding)no one ever complained! But yes, HT and Series One amps all have low Z PI/drivers, C:10k. This is more to keep grid leak resistors low because of the very high, very variable grid current found in modern valves.
But yes Will, if you read the various texts about blocking distortion virtually all guitar amps should sound pants. Somehow they don't!