config.htmlTag_setParams overrides all existing attributes
The new Site handling functionality should ideally avoid
TypoScript conditions as much as possible. However,
if someone wanted to add attributes via config.htmlTag_setParams
all language-dependant properties (e.g. dir and lang) which
are generated by the site configuration are gone, leading to the
way of having to workaround this issue by using stdWrap or conditions).
So, in order to add a "amp=true" attribute to your HTML tag, you need to add
conditions if you want to keep the "dir" (language-dependant) attribute as well.