Distributing flights around the regions would be incredibly beneficial, I agree. However, the major flaw in that plan is that there is nothing stopping them doing that now,given that none are anywhere near capacity...and yet, all the airlines want to be at LHR.
Why? Because of hub connectivity. A large proportion of pax at LHR are transfer pax (as we know) and make routes viable that otherwise wouldn't be. This is the reason hub airports exist, and why all thr airlines all want to be at LHR, even though it would be cheaper to operate from elsewhere