User blog comment:MisterWoodhouse/The first migrations to the Unified Community Platform/@comment-76.187.10.116-20201225231607/@comment-1038387-20201225233749

Images can be used as many times as you want and be given any size you want.

Editor doesn't bounce. Stop trying to make that a thing. Elements may take a bit longer to load and push down content, but it doesn't go back up.

There is loading lag, but at what point does that become "severe"?

Yup, chat is gone and Forums are changed. While it may have been popular on some wikis, it was very limited, relied on hacks and had little future code wise. For Fandom, there were acceptable alternatives. Forums being gone is independent from UCP, UCP is just the nail in the coffin.

There are plenty more valid concerns with UCP (though I'll give you lag). Limited documentation, spacing, WikiActivity, overreliance on custom elements, still poor mobile performance. But those are elements that can be improved in the future.