My counterpoint to these arguments is that less is more.
With 6 characters you can cover all bases, use all gear, easily optimize your tactics, see through most companions stories to completion, etc.
Having only 4 makes choosing your party have much more tangible implications and makes many choices more meaningful. If you can't fill every conceivable party role or have every spell you might need, tactics matter a lot more than if you had the expansive breadth of options you get with 6 PCs worth of tools.
