So net advantage to BRK:
>$10B chemical business
$2.12B OXY debt pay down
$3.2B OXY cash infusion
———
Total benefit $15.32B

I agree that there are some potential benefits, but I don't think that list is a good way to look at it.
At a very minimum, don't forget the ~$10bn cash going out the door.

If we take as a first approximation that Oxychem is being bought at around fair value, the value of an Oxy common share hasn't changed (perhaps even down a bit because of the tax hit from a cash sale), and the cash leaving the door at Berkshire exactly balances the value of the Oxychem business being bought. Maybe Berkshire is paying a little less than true fair value(and maybe not), but that's a second order effect at most.

What has changed, mainly, is that Berkshire now owns a whole lot more of the (existing) Occidental. The same ~27% fraction of the non-Oxychem business, plus now all of Oxychem instead of ~27% of it. If the acquired business accounted for 1/4 of the value of a prior Oxy share, then we now own something like 45% of the old combined business, before exercising warrants. (100% of the 25% which was Oxychem, and still 27% of the other 75%).

Jim