As a well seasoned web developer, when I'm doing front-end, there are always 2 big problems: Data tables and loading indicators (fun way of saying it's hard to tackle lazy loading without a request waterfall).

The second problem has had good attempts in the recent years, but no single web application can beat excel in terms of data tables (while not 100% relevant anymore, I really like the super light introduction here from Joel Spolsky: https://www.youtube.com/watch?v=JxBg4sMusIg )