My understanding is that thinks C++ sucks period (an uncontroversial opinion even among C++ devs).
His reasoning was that C was a pretty minimalist language introducing structured control flow and little else, yet it's flexibility and neutrality has allowed people to explore lots of approaches.
C++ on the other hand is highly opinionated, and a lot of its opinions are considered wrong or at least controversial (template metaprogramming, RAII, exceptions, diamond inheritance, just to name a few).
A lot of the C++ community doesn't use these features (for example Chrome, LLVM have exceptions turned off).
Jai on the other hand goes heavily into typed AST macros (along with a reasonably powerful type inference enigne), a very powerful extension of the language, that this language has gotten right - the feeling you get when looking at the docs is 'well, duh it obviously has to be done like this' - considering how long it took devs to arrive at this system suggests this is far less an obvious task than it looks like.
Other than this, what the language offers over C isn't much - it shares Odin's 'context' idea that you can inject an allocator or logger function and have your methods use that - which is kind of the point imo.
Blow, as outspoken and controversial a figure he is; seems to have designed a pretty unopiniated language - something designed for master programmers (like ones he has worked with in the games industry, who worked mostly in C) to express themselves, rather than a set of 'correct' opinions the language imposes on you.
Imo it's a shame it took so long to release, as I'm p. sure Jai would've been much more influential 2-3 decades ago or more, and would've had a good chance to dethrone C++.