The paper in question is now published at
http://www.nature.com/articles/s41586-018-0025-2
but you will need to pay or have a subscription.

I am reluctant to respond further, but there seems to be one point of
confusion I can clear up:

In article ,
jacobnavia writes:
how can you make a cluster of this mass in only 1.2Gy?

As noted, the models do so, as shown in Fig 2 (right panel).

So the models do not fit at all for the left panel.

Which shows something related to linear size. As was stated in the
paper, the models for cluster size omit galaxy interactions, which
will (it seems) make real clusters smaller than the models say.

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