Pretty much all my 2C-X experiences were RCs from that 2003-2004 era. I notice the doses I needed were less than what some of the more current amounts that people take. I mean 37 mgs of 2C-C had the room swirling in blue and green patterns. It was pretty strong and I am not that sensative to psychedelics. So it makes me wonder when someone says they did not feel much from 50 mgs. Of course tolerance factors in but I was always curious as to what others thought about the different time periods. I know about nothing of what is out there today.
2C-C natural tolerance varies a lot. My early experiences with it were when I was younger and I just was a hardhead moreso than now. My first experiences were with a supply from one of the OG high quality vendors, and I was requiring 50mg or more to really get somewhere, even though I can really enjoy and get a lot out of even 20mg now, and 35mg is extremely strong. A lot of people back in 2001 and shortly later years were reporting needing 60mg. Actually the average reported dosage for 2C-C seems to have gone down. But in general I would say you're right. 2C-C is an oddball and I think some early Erowid reports and online discussion included some idiosyncratic reactions, and there wasn't a lot to go on, as it was one of the less popular ones (I believe based on a number of prominent report writers who did not care fort it and reported it as bland, whereas some of the other 2C-Xs were given glowing reports).
In general the quality of RC psychedelics has not suffered these days nearly as much as other types of drugs. Much of what is being produced is still very high quality. The tryptamines are almost all produced by one very well respected vendor (though some of their synths with other things and a few of the new tryptamines like the -PiPTs seem to be rather poor quality recently) and the quality is as good as it's ever been. The 2C-Xs that have been produced in the past decade (that only stopped recently) are as good as I've ever seen, too. Though selection is vastly reduced. The 2C-E I got before it disappeared from the last source I know of is amazing quality, as is the 2C-C and 2C-D.
The drugs that really suffer a lot are the ones that are more popular/higher volume. The stims, opioids, benzos and dissociatives are hit or miss, with some truly awful batches (especially the stims, there is some absolute garbage out there).