Williams hasn't condemned the ECUSA exactly, mainly since it's an open secret that he's in almost entire agreement with them substantively if not procedurally; not all of the Catholics are going to Rome (and there are also Roman Catholics who come into the Communion out of disgust at how Rome does things); and as long as the Church of England is culturally closer to the North American Churches than to the African Churches the likeliest result is an eventual fracture between the liberal/Anglo-Catholic factions and the Evangelical factions, not the Evangelical factions taking over. Honestly, I don't see why we need the Evangelical factions, spiritually speaking; they can just bugger off and become Pentecostals if they keep being ungrateful to the Instruments of Unity for covering for their sorry asses. A Communion run by the Evangelical factions is a prospect that simultaneously baffles, sickly amuses, and terrifies me.
The proper head is of course the Archbishop, and the Queen has no authority whatsoever, even technical, over parts of the Communion other than the C of E.
His constant warnings to them have gone completely unheeded. Whether he agrees with them theologically is immaterial, he realizes that the actions taken by the ECUSA (and to a lesser extent the Canadians) are the real cause of disunity in the communion. If there were any avenue through which the ECUSA could have been punished it would have been, I don't see how anyone can argue otherwise.
The problem is that there is no mechanism for the Archbishop, short of breaking off communion. The Episcopal Church, since the 1783, gives him no role in the church, to the point that the first American bishop was consecrated by the Scottish Episcopal Church. It was founded, in part, to be separate from control by the Church of England.
A "takeover" would be totally irrelevant at this point. Yes, the evangelical wing is "vibrant" in its own home. The US is not one of those homes; I'd doubt that the UK is either.