Linking to that GitHub issue is pretty embarrassing for you. Not only can it not be practically exploited, per the author of that issue, but it looks like it's just using Keccak as a stream cipher of sorts (but seeding it from /dev/urandom). That's pretty ok, and if we don't trust stream ciphers to produce pseudorandom numbers we have much bigger issues.

But more importantly, the contributors acknowledged the issue, and are fixing it. Do you honestly expect bug free open-source development? No, and the entire benefit of it being a welcoming open-source development community (instead of ZCash's centralised development team) is that it is made better by many eyes. Hopefully the OP that opened that issue spends some more time reviewing the code along with the 160+ Monero contributors.

Also, if we're going to view lapses like these as representative of a major failure, you'd best review some of ZCash's greatest hits, maybe starting with the fact that wallet encryption is ENTIRELY DISABLED in ZCash, and your wallets are stored in the clear and ready for malware to steal: https://github.com/zcash/zcash/issues/1552

- https://github.com/zcash/zcash/issues/713 <- this one is particularly stupid, and shows a gross misunderstanding of how Bitcoin works

- https://github.com/zcash/zcash/issues/1304

- https://github.com/zcash/zcash/issues/1522

- https://github.com/zcash/zcash/issues/1779 <- literally, they had ONE JOB for the release, how did they fail at that?

- https://github.com/zcash/zcash/commit/f8ada2435bd3f6b7a1165e... <- oh that's right, they failed at the one thing they had to do because they were focused on other...uhhh...important stuff

And let's not forget the massive attack surface that ZCash has, which leads to fun things like this:

- https://github.com/zcash/zcash/issues/98

- https://github.com/zcash/zcash/issues/178