Here is why I (respectfully) say you are wrong. Rubio and Paul do not benefit from trying to take votes away from Cruz. The big opportunity tonight is to steal take away Trump supporters. Trump has the biggest piece of the pie. Cruz supporters aren’t going anywhere.
Also, it will be interesting to see Jeb go after Rubio. Bush PACs are spending $1 million dollars per day ripping Rubio. It has had little effect. It is relentless.
If Cruz can be taken down in Iowa, he is essentially finished. The group of sharks on stage will be dedicated to doing just that. Then they can concentrate on Trump.