What you say is true in the same way like saying that taking a cup of water out of the ocean lowers the ocean level a little. It is true, but it is not significant. The moment the mining is moved to mostly non-solo miners ( and even now non-solo miners seem to vastly outnumber in sheer mining power established solo miners ).

Basically, concentration of power means that eth will quickly become everything the banks are.. only worse ( because with banks you at least have some regulation to back you up ):P