Yeah, that is what people like to think. But when they support the use of bots openly, it is no longer a good excuse for doing things that affect players negatively in my opinion. The bots are still going to just farm credits and then buy cards and sell them for DEC.
This specific change really is not all that bad. Depending on the credit reward amounts, a bronze player's earnings probably aren't going to change too much.
RE: Game Economy & Reward Updates