Not a single developer I know (I was in leadership position in a company with 300+ devs, now I lead a small startup dev team) cares about "heyday". They care about their experience during development being significantly worse with plain JS due to stupid ("we'll use TS because it checks names of properties") but also not so stupid ("we'll use TS because it checks that switches are exhaustive", "we'll use TS because it allows you to check nominal types") mistakes and bugs that TS helps to prevent. For all the devs I know, hearing that they have to code plain JS is the point when they head for exit.

I never said people would "choose" TS because it's in its heyday, I said it'd be an unlikely time for most to wish to justify a switch back.

Most of the types you write in TS will be structural

Indeed, but the few ones that are nominal are making the difference.