Never said you can increase CID through rpm, just what an engine actually displaces the displacement/volume of air per minute, CFM which is cid x rpm / 3456 = ve% which Cid is part of that process. I see CFM as a measure of displacement.
Agreed, a 340 basically always be made to be spun slightly higher to displace the same cfm as a 360 and a 318 can't cause a 318 & 340 always can be made to spin the same rpm. But for the average 300-450 hp build there all capable.
I know people who still feel that way