> 60% (II) with 18% (ICMS) on top for a total of +88%

Nope. ICMS is calculated "por dentro". It's base / (1 - rate), not base * rate.

     Product = 100
          II =  60
             = 160

  ICMS total = 160 / (1 - 0.18)
             = 195.12

        ICMS = 195.12 - 160
             = 35.12

That's +95.12% tax. Also known as nearly 100% tax. One for me, one for the government.

> The tariffs for commercial importations are much lower and depend on the part.

Fair point, but they're sure as hell not "much" lower. As you yourself noted, they are still high, and obviously those companies are going to want to add their own margins on top.