list pages using page.php and NOT page-{slug}.php

I believe you need to use get_template_part, but you need to request the get_page_template_slug first.

So that would look like:

get_template_part( get_page_template_slug( get_the_ID() ) );

in lieu of

echo get_page_template();

And no need to echo it, it returns the template already printed.