Burden of proof on the accuser is not a "legal technicality", and what level of wealth would you suggest should flip the burden of proof?
We're confusing two things here:
1) Could they have copied his stuff?
2) Did they actually copy his stuff?
No. 1) is clear: He published his work. CBS most definitely could have accessed and copied his stuff.
Thus, the court should go into phase 2): Did they actually do that. Which would be pretty easy to prove by just looking at the series bible from an earlier development stage.
But what CBS is trying (and succeding at) is making the burden for (1) SO high as to realistically impossible: FInd the exact person that saw your stuff and copied it, out of a million dollar company - basically the guy has to present enough evidence to unquestionably win the case before the case even actually starts - that they try to evade the actual part (2) of the investigation. And that is simply not fair.