That's very true right now however if Steem ever becomes more valuable than SBD you'll want to take your post payout as 100% power up.

Currently, Steem is worth $6.31 while SBD is worth $6.96 (this is the closest in value the currencies have been in a long time). So it still makes sense to do a 50/50 payout.

If SBD goes lower while Steem continues is climb in value, then converting to 100% payout in Steem Power makes a lot more sense.

Hope this helps!