TFA complains about "marginal income rates of %43" as though this were the general case. For what it's worth, %43 is the highest capital gains rate, the highest income rate is %39, which is for incomes of over 1.8MM: http://en.wikipedia.org/wiki/Income_tax_in_the_United_States
With that out of the way, the highest marginal tax rate was around %90 during the boom of the 50's and 60's, and is lower now than during Regan administration for example: http://www.ntu.org/tax-basics/history-of-federal-individual-...
If one is a member of the very highest tax bracket, then one might be tempted to measure freedom by the myopic comparison of income tax rates. It would be unsurprising if the Heritage Foundation were concerned about the very highest tax rate in great disproportion to it's nominal consequence.
There are other economic freedoms: freedom from excessive gov't granted monopolies (patent/copyright), freedom from protectionism, tariffs, limited work visas, etc. Even rich guys driven to distraction by high tax rates ought to be able to find something say about these sorts of things in an article about economic freedom, but no specific structural reforms are proposed. News flash: partisan think tank doesn't like taxes, president.
For the rest of rest of us, real freedom also means not being imprisoned for interacting with other consenting adults in ways that are illegal, and not being denied due process in various ways such as: torte reform, civil asset forfeiture, being spied on by agencies who are immune from judicial review, etc. Could we take a break from wringing our hands about the welfare of the ultra-rich, and work some of that stuff too?