You might be misunderstanding the purpose of the hundred million dollar rule. It is an arbitrary threshold, that’s true; any threshold would be. But what it triggers is just an extra step that the FTC must go through where they receive suggestions from the public, including the industry to be regulated, for _alternatives_ to the proposed rules. They must then go through and determine for each of the alternatives whether it would be effective at achieving the goal of the new regulation, and if so whether it would be cheaper to implement than the proposed rules. If it would be both effective and cheaper to implement, then the FTC is supposed to drop their own proposed rules and adopt the alternative rules instead.

So for example if the proposed rules said that everyone selling any kind of subscription must do X, Y, and Z, and Z was pretty expensive, then you might write in and suggest doing W instead of Z. If W would be effective and cheaper to implement than Z, then the FTC is supposed to change their proposed rules to require everyone to do X, Y, and W instead.

There's just not much reason for this step to depend on how much fraud the new rules would prevent. The public comment period and the analysis steps only take a few months, and in the grand scheme of things a few months is not much time at all.