Obviously Wordpress might seem like total overkill if you only need a single "coming soon" page - but ultimately you'd be able to make this a lot quicker with Wordpress than with anything else.
If you have CPanel and similar hosting you can install Wordpress usually right from there, log-in to your new WP install, get such a plugin, activate...and DONE.
Probably in the time that requires someone else to start-up their HTML editor

So yes, Wordpress all-the-way.
** Depending on the "theme" for Wordpress, don't know whether the "coming soon" plugin(s) are already responsive - but then simply install a responsive theme. Also a matter of 20 seconds. Wordpress IMHO is the best choice, no matter how simple or complex.
** Edit yes I forgot about Wordpress.COM <--- so even more simple!
(Wordpress.org is if you want to self-host on your domain, eg. by manual installing WP or from Cpanel, most modern hosters should have an option that you install it from the panel)