After a brief glimpse of the rant you linked - where the author claims 'that's bogus', '[they're] wrong', 'dead wrong', etc. - I'd say that you're better off taking the argument with a grain of salt.
There are circuit-dependent factors that can affect the usefulness of any thumbrule. Any determination aught to be done with a specific amp as an example, only then can any general case be extrapolated. Some amps can operate in the envelope with two tubes pulled, others may be over-dissipating. A cathode biased amp will change the bias operating point (not sure if there are any examples of a cathode-biased 4-tube amp?) and need compensation.
As a general rule (after advising you to be suspicious of general rules) pulling two tubes and moving the load to the next lowest impedance (thereby doubling what the reflected primary Z sees) should keep the amp inside the designer's operating envelope.
If your objective is to optimize the amp's behavior with 2 tubes versus 4, then all the technical suggestions come into play. Bias, check plate and screen dissipation, check output signal, etc. But you'd likely take some of those steps with any simple tube change.. if it's the tone you're chasing.