Offset Page Loops and Pagination

I have really been struggling with getting the main loop for the index.php to work properly with WP_Query functions. I need the grid array of 6 featured images at the top to not be offset at all, while offsetting the main posts loop below it by 6 posts.

Anything involving query_posts() inevitably ends up breaking the pagination. Using a single loop fixes the pagination issue, but undesirably applies the offset to the featured grid section. I have managed to get the pagination main loop to work using WordPress codex's recommended fix of pre_get_posts https://codex.wordpress.org/Making_Custom_Queries_using_Offset_and_Pagination. However, this fix overwrites the featured posts loop settings by 6 as well.

The offset/pagination dilemma seems to be a well known issue to WordPress developers, and I've browsed dozens of articles, forums, and tutorials but I can't find much documentation on what to do when the pre_get_posts fix overrides other custom loop settings on the index. The pre_get_posts works to a degree, I just want the formatting to only apply to the main posts loop on the home page, not the top 6 posts.

Here is the code. Thanks for taking the time to read this.

index.php:

?php get_header(); 
do_shortcode( '[mg-masonry_js]' );
$options = get_option('mg_options');
$option_cats = $options['mg-posts-categories'];
$option_pg_number = $options['mg-posts-post-per-page'];
$args = array(
    'post_type' = 'post',
    'post_status' = array( 'publish' ),
    'posts_per_page' = $option_pg_number,
    'orderby' = 'date',
    'order' = 'DESC',
    'cat' = $option_cats,
    'offset' = 0,
);
?

div id="all-content-wrapper"
div id="home-content" 
div id="grid"

?php if ($paged  1 ) {
    $paged = get_query_var('paged'); ?

?php  // initialize main loop  ?      

?php   $grid_query = new WP_Query( $args );

    if ( $grid_query-have_posts() ) : 
        while ( $grid_query-have_posts()) : $grid_query-the_post(); 
?

        ?php   switch ( $grid_query-current_post ) {
                case 0 :
        ?
            ?php  // First featured image code here    ?
            ?php   echo get_template_part('grid_featured');    ?

                ?php break; ?

            ?php  // Grid image array code here    ?  
            ?php default : ?
            ?php   echo get_template_part('grid'); ?

        ?php } ?  ?php  // end switch ? 

    ?php endwhile; 

wp_reset_postdata(); 
rewind_posts();
else : ?
        h2?php _e('No posts.', 'news portal' ); ?/h2
        brbrp class="lead"?php _e('No posts to display.', 'news portal' ); ?/p
?php endif; ? 

?php  }    // end paged switch ? 
/div   ?php // end grid ? 

div id="primary" class="content-area"
    main id="main" class="site-main" role="main" 

    ?php
        $args = array(
        'post_type' = 'post',
        'posts_per_page' = 10,
        'offset' = 6,
);
?

?/* Start the Loop */?
    ? $main_query = new WP_Query( $args ); 
    if ( have_posts() ) :

        while ( have_posts() ) : the_post();

            get_template_part( 'template-parts/blog', get_post_format() );

        endwhile;

        echo regular_pagination();

    else :

        get_template_part( 'template-parts/content', 'none' );

    endif; ?

/main!-- #main --
/div!-- #primary --

?php news_portal_get_sidebar();?

/div!-- #all_content_wrapper --

?php get_footer();?

functions.php:

/*--Offset Pre_Get_Posts pagination fix--*/
add_action('pre_get_posts', 'myprefix_query_offset', 1 );
function myprefix_query_offset($query) {

if ( ! $query-is_home() ) {
    return;
}

$offset = 6;

$ppp = get_option('posts_per_page');

if ( $query-is_paged ) {

    $page_offset = $offset + ( ($query-query_vars['paged']-1) * $ppp );

    $query-set('offset', $page_offset );

}
else {

    $query-set('offset',$offset);

}
}

add_filter('found_posts', 'myprefix_adjust_offset_pagination', 1, 2 );
function myprefix_adjust_offset_pagination($found_posts, $query) {

$offset = 6;

if ( $query-is_home() ) {
    return $found_posts - $offset;
}
return $found_posts;
}