>The idea here is that the casino will be more diligent in not tilting the odds too much in favor of the whale

Allowing scripted entries is one of the biggest examples of this and a huge differentiator between DFS and casino games like poker. You will very rarely have an absolute poker novice playing against a skilled shark. The novice will generally know they are a novice and will enter lower stake games. The shark's time is money and they will only enter games with high enough stakes to merit playing. This is completely different for DFS when scripting is allowed. The sharks can play an almost unlimited number of games against any opponent. If it is completely automated, there is no reason why the shark can't challenge the complete novice who is only willing to bet $5.

DFS sites do have novice games and ones with limited entries per account, however. You can choose to enter these.

Trust me, it isn't the "Casino's money" it is always the other players money. At its most simplest, people come into the Casino and drop money on the floor, the Casino collects it, and then randomly gives some of it to people as they exit. It preferentially (by giving a higher probability) gives money to people who have come in a lot and have dropped a lot of money on the floor. At no time is there any risk that the Casino won't keep all of its "fraction" of the dropped money.

There is always risk, a series of unfortunate events can drain a casino, the casino tries to mitigate these risks through the rules/odds.