My question is how significant that affect the cantilever to be stiffer and introducing possible tracking issues, OR its effect is negligible?
Your target for mechanical resonance is between 7-12Hz. The mechanical resonance is a product of the mass of the cartridge in the arm vs the compliance of the cantilever of the cartridge. Changing the load from 47K to 100 Ohms can easily get you outside of this target window- and that can cause tracking problems.
So, all those very well regarded designers are wrong?
IF they have ignored the significance of the inductance of the cartridge in parallel with the capacitance of the tonearm cable in their design
THEN yes, they blew it.
If you doubt this I recommend a simple test, which is to run a square wave through the cartridge itself and observe the results on an oscilloscope. If the square wave rings, then loading will affect it at audio frequencies. If you do this with any LOMC cartridge you'll see that the inductance of the cartridge is so low that a square wave at any audio frequency will look perfect on the oscilloscope. So its obvious then that the loading isn't affecting the tonality of the cartridge. Something else is.
So if the loading does not affect the cartridge at audio frequencies, why would it affect how the cartridge sounds- because in some preamps that is quite audible. The answer is simple- the preamp itself is reacting to the RFI generated by the cartridge (hence the emphasis on 'some'). I've explained this a good number of times, I've dropped links to Jim Hagerman's site http://hagtech.com/loading... If the preamp is designed with the RFI present at the input of the phono section, the loading resistor will make little difference- it won't tone down the high end nor will there be a need; it will sound fine with a 47K load.