The Federal credit effectively drops their net take all the way down to 0.8%, not 6.2%.
Its limit is so low because Congress has never revisited it in scores of years. In the beginning $7,000 was real money.
The 6.2% language was crafted to compel each state to adopt its own program without triggering a Supreme Court case in the FDR era. That's because the feds were clearly legislating labor practices long the exclusive domain of the states.
As a side note, the unemployment tax and benefit was adopted promptly after it worked for NAZI Germany. A connection that is rarely mentioned today. In fact the system went world wide in the 1930s.
State rates run all the way from 2% to 8% depending on who, when and where. The rules are set and reset by the state legislatures -- particularly the caps and payouts -- practically every year.