For me, "high-performance TypeScript framework" implies that it's high-performance compared to other TypeScript frameworks rather than high-performance period. In the benchmark pages (https://deepkit.io/benchmarks), the components of the framework are compared to other TypeScript libraries, which seems to support my theory. But your interpretation is valid too, I think. English is a second language for me so I'm not sure if this is something up for debate or not.
Yes, that is what is meant, also in terms of development speed. Of course, there will always be faster implementations in other languages, but in context of JavaScript/TypeScript, it's high performance. In the introduction blog post can be seen more about why this is: https://deepkit.io/blog/introducing-deepkit-framework