It really sounds like we're comparing apples to oranges... one might consider "tuning opportunity" as "unnecessary complication". I came in late to the game around 2010, so the only brushed racing I saw was Spec motors in sealed (non tunable) cans... the extent of tuning we had was using comm drops and that was it.
I began racing in 1984, have seen a lot of things come and go.
I'd like to see a break down of each tuning attribute and see how things have changed with the migration to brushless racing dominating the market. If brushed motors were so much better, then I don't understand why they are no longer marketed for racing anymore?
Windings - Did folks actually make their own stators for brushed motors? Current brushless manufacturers sell replacement stators, is this not the same thing?
The armature of a brushed motor does the job of stator in brushless. The equivalent of a 7.5 stator in a brushed armature was available in several different winding options.
Timing - With brushless motors, this is adjusted by rotating the sensor board and measured within 1° of accuracy across all 3 phases with a motor analyzer, how was this adjustment made with any accuracy on brushed motors?
Timing phases are perfect on armature. Timing was adjusted by rotating the whole endbell.
Shimming - Pretty much the same, you want the bulk of the rotor centered on the stator, the motor analyzer shows you how perfectly centered you are as the reading of all 3 timing phases get closer together... how does this work with brushed motors?
similar. Had less to do with timing accuracy, more to do with magnetic field.
AirGap - I don't even know what this means, please explain more on this and how it can't be adjusted with brushless
Gap between armature stack and magnet. On brushless, this is adjusted with rotor diameter.
Brush hardness/cut, spring stiffness, commutator diameter - These are elements of gross inefficiency that were eliminated with brushless
Brushless is unquestionably more efficient. Brushes and their replacement were a tuning option that we no longer need to think about.
Armature Stack - I have no idea how this is tuned either, please help me understand this better too.
similar to stator stack. Armature were available in non-standard stacks (mostly sealed stock motors).
Something that I see very common with brushless motors today is the ability to swap out various rotors to tune magnetic strength to get more torque/acceleration or transfer to a different rotor which provides higher RPM depending on track conditions. Was this done the same with brushed motor racing too?
When did ceramic bearings first come out? That is another tuning option that I've seen with brushless motors.
they've been around a very long time. More fragile, but good for high rpm, lower load applicatiins.
I've also seen non-magnetic titanium timing plates marketed as a tuning option for brushless motors to improve performance.