As someone who only used Onlyoffice briefly, to me they both seemed to do the same tasks about as well as each other. I didn't notice Libreoffice's age except in the settings menu. For actually just doing normal stuff, like word processing, it felt comparable, besides some minor stylistic UI polish in Onlyoffice.

Are there any specific pain points in Libreoffice that you can recall that Onlyoffice does significantly better in?