In scenario 2, government has higher revenue, not lower.

If high earners had to exert themselves twice as much or otherwise expend twice the resources to earn $20 instead of $10, maybe ending up with $9 instead of $12 would be rational. Of course in the real world it rarely works that way, only a few are in a position to work less to earn fewer commissions or work less overtime to avoid entering a higher tax bracket. The brackets are also a lot more graduated, it's not like you could earn $19 and pay $1 tax.