Nope, CGI::Application is a way of modularizing your code by splitting it up into screens (one sub per screen/action).

Not having to write a giant if/elsif/elsif/else to separate your screens is a huge timesaver.

Very pointy

Working on the assumption that you would already have one sub per action (which probably calls several other subs in turn) and merely use the id/elsif/sleif/else to decide which to dispatch to, then I still fail to see what benefits CGI::Application gives you.

From the documentation, you are expected to do this:

sub setup {
        my $self = shift;
        $self->start_mode('mode1');
        $self->mode_param('rm');
        $self->run_modes(
                'mode1' => 'do_stuff',
                'mode2' => 'do_more_stuff',
                'mode3' => 'do_something_else'
        );
  }
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which really is just another way of writing this:

if    ($cgi{rm} eq 'mode1') { do_stuff }
 elsif($cgi{rm} eq 'mode2') { do_more_stuff }
 ...
[download]

it's just different boilerplate.

The $self->run_modes stuff takes care of the HTTP headers for you, which is the exact problem the OP has. So its much more useful than a large conditional where you claim it is identical.

If you don't like configuring the runmodes in the setup method, you can just use CGI::Application::Plugin::AutoRunmode.

Also, once you go with CGI::Application, you immediately have all of the plugins that others have shared on CPAN so you don't have to keep reinventing wheels that have already been done better by others.