Enabling all HTML means that any user can embed JavaScript into the page which can then be used to exploit vulnerabilities in the visitors' web browsers, e.g. to take over visitors' machines. Wiki admins may not be aware of this and inadvertently turn their Wiki into malware spreaders.
If you are sure that this is not a concern for you, you can simply install one of the "HtmlOK" plugins (there are at least two of them) which basically re-enable the old feature 1:1 - or you can use my own "Ad-Hoc Tags" plugin, which takes a more selective and sanitised approach and allows you to chose which tags you allow in your wiki (and which modifies the syntax to become more "wikified")
It is not that you are left without any options. It is just that if something goes wrong with your wiki, it is your fault that you installed these plugins, and not because there is some easy to misunderstand option in the config that you have enabled without being warned about the implications.