Can you check where I'm going wrong with this? Here's how I looked at it:
Let BG and PG be two random variables, BG is the house's bankroll growth and PG is the player's bankroll growth (in absolute numbers). Then:
BG + PG = 0 (money only moves back and forth between the house and the player, so a loss for one is a gain for the other and vice versa)
It doesn't make sense to sum those growth multipliers.
Obviously, and that is indeed the reason why I'm not summing them. I said "in absolute numbers" multiple times now. Anyway, I'm pretty sure my argument is correct, especially since the edge case trivially shows that it is indeed possible for a player to be -EV and +EBG.