I think the bankroll hasn't changed too much. It's just the bustabit has used the terminology "bankroll" to mean "onsite + offsite", and on the 15th of December everyones offsite was set to 0 (and they were given dilution fee credits for that amount). So the bankroll dropped a lot, but the amount "onsite" stayed the same.

It'd be nice if the /stats page showed the commission directly, but currently the bankroll is 4956 BTC, which means the commission is 49.56% (or slightly less than before the change). On bustadice, the bankroll is considerably smaller (1977 BTC) which means commissions massively dropped to 19.77%.