Somebody says it's possible to disregard point C provided I can demonstrate through performance calculation that in case of RTO the airplane can come to a complete stop well before the end of the runway (?!?)
Yep. If the ASDR is short enough that you'll stop before entering the last segment of the runway, then the last RVR can be disregarded as it's not relevant.
I think the key is in the wording... "The required RVR value must be achieved for all of the
relevant RVR reporting points with the exception given in Note 3 above" - Appendix 1 to EU-OPS 1.430 (Note 3 being the bit about pilot assessment at the start of the runway)