The Babel team is great.... and they're also tiny, overworked, and underfunded. (See some of Henry Zhu's recent conference talks on dealing with being an OSS maintainer for background.)
I think Babel 7 had some perf improvements (including tweaks contributed by Benedikt Meurer from the v8 team), but I don't think they've ever had time to focus on just improving perf.
I think Babel 7 had some perf improvements (including tweaks contributed by Benedikt Meurer from the v8 team), but I don't think they've ever had time to focus on just improving perf.