That's true - but taxes *always* disincentivize the thing being taxed. If investment in a company is less profitable under taxation than it otherwise would be, there will be less investment in that company, no exceptions. Now the size of that effect is quite likely to be negligible for the companies in question here. But it's at least theoretically possible that taxing corporate profits could lead to a change in the marketplace, including market dropout, that might actually lead to consumers paying higher prices to the remaining members of a market with reduced competition.

Further, if all companies in an already low-competition marketplace are equally affected by the tax, then it's quite possible for all of them to ~simultaneously raise prices to offset the tax, with or without explicitly illegal coordination, knowing that the others will follow suit.