I think the Doc has got you bang to rights on this one Crash. As he says "From the example given you wrongly presume both punters (all punters) lose." Your quote outlined above shows what he says is correct.
Punters who (successfully) punt in order to win money don't have the odds against them. If they win long term they obviously have the odds in their favour, so you are assuming your fictitious punters are losers.
If a punter has a winning system and he bets on more races which fit that system he stands to win more. If a punter has a losing system he stands to lose more from betting more races. It's simple.

KV