Find me a business of any size which isn't on the fiddle - sorry, exploiting allowances, tax classifications, and loopholes to the very maximum extent allowed by law. You have to do that in order to survive, or your competitors will eat you alive.
So closing loopholes in order to reduce the headline rate of tax is at best a zero-sum game for any real business, depending on how much the headline rate comes down (if any).
This might be viewed as bad news for accountants, but it's quite the opposite, since they'll just have to work harder (and bill more) to find the remaining - and doubtless some new - loopholes.
The tax code needs re-doing from fresh, starting with a flat rate and no (nada, zero, zilch) wheezes or loopholes, not yet more token fiddling around the edges.