I'm not seeing this at all. I can reduce Opacity or Flow, then build up gradually with the brush with Smoothing enabled in Brush Settings and a higher number set for Smoothing on the Options bar. Could you be more specific about what brush settings you're using—perhaps show us a screenshot that shows you can't increase the opacity of a brush with repeated strokes?
It's also possible, of course, that between one version of PS and another, you need to delete your preferences since they may not be working well together. Have you tried that (first saving any custom presets you've made)?