Is Starkware a threat to Zcash?

yes, the ZF has a wider goal list than the ECC, which is what led to some questions about how the ZF could/would spend money that offended some people, but the ZF seemed to reply that their focus is on zcash.

And the ECC is who funded starkware, not the ZF.

https://electriccoin.co/mission/

And the ECC’s mission is solely on zcash and spreading zcash adoption.

Edit: These are the posts I was referring to about ECC vs ZF’s missions and concerns that came up, which showed that the ECC focuses on zcash only (or partnerships that help zcash as well)

https://forum.zcashcommunity.com/t/thoughts-on-conflicts-of-interest-within-the-zcash-foundation/41679/3