Custom Path HomePage URL

[WP 4.8.1, WooCommerce, Wp SuperCache]
Hi,

I have a site with custom path homepage url, eg.
instead domain.com home page url redirects to domain.com/custom-path

Wordpress is installed in webroot directory. It’s just that homepage has a custom path instead of default webroot/domain url.

It is done by 2 rewrite rules in .htaccess:

# 301 due to filters off
RewriteCond %{HTTP_HOST} !^www.domain.com(.*) [NC]
RewriteRule ^(.*)$ https://www.domain.com/$1 [R=301,L]
# 301 homepage
RewriteCond %{QUERY_STRING} !^/?s=(.*) 
RewriteRule ^$ /custom-path [R=301,L]

and also by a filter added to functions.php (it removes default template redirects)
remove_filter('template_redirect','redirect_canonical');

We serve WP-Super Cache versions of urls to users. The trouble is that since custom path homepage url is in place we see more latency, and much longer server time response.

I fear that Super Cache somehow gets confused which page to serve causing latency in homepage cache serving. Other website pages do not have this latency – we monitor it.

Now the question: Is there latency friendly way of implementing custom path hompage url which would not cause delay in loading homepage cache? Could anyone put me int right direction?