i feel dancer and mojo simplify things to the point you dont need to know the basics any more.
Yes and no at same time.
They are frameworks written in Perl to produce web applications written in Perl: they aim to hide you dirty work and they aim to do the right think unseen. Are easier to use? comparing to old CGI's? This is up to you. For sure are easier to use if you wont do the right thing with a secure, stable, deployable, maintenable, inspectable.. web application.

While Dancer2 (yes now is Dancer2 please search for it) is simpler then Mojo there is always a lot to learn.

The central point is: Mojo and Dancer2 and other modern tools let you to use PSGI. That protocol, specification, is the ribirth of Perl in web context: CGI was good in the past, but, sad to inform you, is dead.

Search around for PSGI (the specification) and Plack (the implementation) you'll realize it too. While you can write a web application entirely by your own in the rails of PSGI, is more sane to use a framework that make your life easier.

HtH
L*