That's a start-up style marketing: when you make a product you focus on a big vision and positive sides and de-emphasize weaknesses. I'm afraid that's actually 100% Victor's decision to do it this way, and it seems to be working in terms of generating hype: it got ~4k likes on X, which is a lot for a new language.

Regarding substantiation -- they released source code and demos. As far as I understand, the weakness is that proofs are very verbose as there are no strategies. etc. However, they are making a separate service for making these proofs using proprietary technology: https://bend-lang.com/bender