I'm a big fan of Web Assembly but I've hated Flash for a long time. Flash apps tended to peg the CPU and shorten battery life on my laptop, even though most were inconsequential to the web pages that used them (ads). Constant security holes left me paranoid. Crashes left me frustrated. I can't count how many times that Flash crashed on me. The UI of most Flash apps left many things to be desired. From a technical perspective, it was also a deeply flawed design with a mediocre implementation from one vendor. Most video sites which use Flash seem to be far inferior to their HTML+JavaScript counterparts, only the biggest sites ever had decent flash players (Vimeo, YouTube), and I've noticed that some Flash video players can't really handle full screen video with the performance that they should. Ugh. I was glad so many years ago when Flash stopped being bundled with the OS, so I didn't need to take any extra steps to avoid it.