This logic is broken.
If RS 100k and Classic RS is 80k and simillar would happen with Classic WoW, then Classic WoW would not have a "small" player base.
If we can play classic and still be able to find groups at any level range, then that's a success. Blizzard already stated they can run the servers with minimal players and we can easily foresee at least 40k pop for Classic on average.
SOOOOOOU