Were any of those using JS/TS? I've seen Bazel perform wonders with many compiled languages, but I'm not impressed with the JS ecosystem.

Nothing substantial, no. I've never personally experienced builds to be so slow to begin investigating bazel as an option for JS/TS.

Tsgo, oxlint, caching dependencies etc. what linear outlined in their blog post would be more impactful for the average TS project I've worked on.