Just so I understand, you're saying that all phono preamps that have a loading switch inherently haven't effectively dealt with RFI issues in their design?Generally, yes, more to the point they've not sorted out how that peak affects the phono section. The loading resistor detunes that peak and so gets rid of the RFI and so the phono section sounds better (usually less bright). But the tradeoff is now the cartridge cantilever is stiffer so not performing as designed.
The thing is, if you talk to digital guys, they complain about ticks and pops. It turns out that many ticks and pops are generated by the phono section if it has poor RFI immunity and poor overload margins. This BTW is an epidemic in phono preamp design; I would think that anyone interested in LP playback would perk up their ears on this one!