Hi there,
The font weight missing from drop-down is probably due to cache (it works on my installation of Pro 1.2.3), try changing the font over and back again, the list of font weight will start to appear.

But this isn’t related to your class helpers issue that’s because from multiple font weight options, you can only choose one to activate under Typography. Hence, those helpers aren’t related to that setting, example, if you set the Body font weight to 400, then the helper that will only work on that is w-400
.
For the helper to work, all font weight should be loaded hence, only usually with system’s font since all weights are already built-in to a browser. What you could do is load your preferred font through @import
, example, you can add this to your child theme’s style.css (before any existing CSS)
@import url('https://fonts.googleapis.com/css?family=Saira+Extra+Condensed:100,200,300,400,500,600,700,800,900');
_ copied from here https://fonts.google.com/?utm_source=google&utm_medium=cpc&utm_campaign=1001467+|+Material.IO+|+Global+|+en+|+Hybrid+|+Text+|+BKWS&utm_term={keyword}&gclid=Cj0KCQjwprbPBRCHARIsAF_7gDZr3WivlPo0wEr_mOJLCj-3n-QQnilQQ7NXHdnndcN5_VL9dSzM0oAaApyEEALw_wcB&selection.family=Saira+Extra+Condensed:100,200,300,400,500,600,700,800,900 _
It will then load all the font with their size, assuming that you also selected Saira Extra
as your font in your font manager. Then you can apply class helpers to your elements.
Thanks!