I think I need to provide you with more information than I believe you have on the subject of the LCR RIAA network. There are actual real advantages that you don't seem to be aware of when you write "the inductors are worst in that stage than resistors"
First of all, only inductors there can make this kind of RIAA network operate at all. It is not just another filter. It is a specifically designed filter to have certain special properties. It is used mostly in tube preamps to complement their needs if you've got the bucks to try it. The two major advantages are: 1) The input impedance into the filter, and hence the load on the first tube, is held virtually constant all the way across the audio band and somewhat beyond. They are usually 600 ohm professional use impedances, but could be designed for other chosen impedances, like 6K I was trying to make once. 2) There is the tightest of coupling from stage to stage because it has minimized the coupling impedance from output of tube 1 to input of tube 2.
RC RIAA stages use large series resistances that degrade signal transfer control on the second tube's input grid. This loose coupling problem really does cause a loss of detail. In fact, there is another problem such that there MUST be a coupling cap added just to avoid excess bass rolloff from grid leakage when you try to "DC couple", or actually "direct series resistance couple". Now you have a dielectric distortion problem operating in low voltage swings, to many the worst thing possible.
At DC, an inductor is zero ohms, and therefore the LCR RIAA filter is well suited for DC coupling (via inductors, of course). The series resistor creates problems unique to its impact, while the coloration of inductors causes problems unique to their impact.
In either case, the RC filter will measure better and give a flatter FR, but for those that have heard the top LCR filtered preamps, they may be colored, but they excel in dynamics and detail, many people calling that dynamics and detail level "state-of-the-art", no question about it. I've read the comparisons and that's how it comes out pretty universally by the different owner's opinions. But they are rare and the lowest price LCR phono stage I've heard of was $15K a few years ago, from Audio Note Japan I believe. I don't know if they even still make it, or it was a passing fad. Phono preamps are the some of the most difficult electronic pieces to do well in stereo, and so maybe supporting the LCR filter was not practical.
The LCR RIAA filter does have C's and R's in it, but those are less critical than the L's.
I have never completed my LCR preamp, and maybe someday I will. But the technical challenges and costs are great. You need support parts that are outrageously pricey and nearly impossible to source in order to make a good implementation. So my preamp is RC filtered still.
Excellent, but still I WANT my MC step-up. I have tried pre-preamps (head amps), but they never sound anywhere close to what I'm looking for. Then again, I like Koetsus, so that'll tell you something about my prferences in music reproduction. I thought the Transfiguration Temper Supreme I had was a cool-sounding rough-riding sterile hard-to-stick-with cartridge, and same to the Audioquest 7000Fe9 I had. Other reviewers said those were "neutral".
Kurt
