User blog comment:MisterWoodhouse/The first migrations to the Unified Community Platform/@comment-917161-20201221104339/@comment-1038387-20201221121051

Performance is a known issue, which hasn't had much improvement since March. The source editors are better than the visual editor, and the 2010 ("Source Editor" in the prefs) is probably the least laggy.

It's possible your issues are ones that have been reported before. Are you talking about originalcharacters.fandom.com? Some of the issues you tried to fix on the main page:
 * Createbox is deprecated, use inputbox with the type = create.
 * Since WikiActivity is retired, the Activityfeed tags are as well. You can still emulate it by embedding Recent Changes with