Prefork is different think with event/worker. Prefork is php embedded (integrated) to httpd itself and that why timeout not most issue. Event/worker is php will be request by httpd to fastcgi.
On Prefork, php instance will be the same with httpd instance (because embedded). In Event/worker, no need huge amount httpd instances (better choose 'default' on 'apache optimize') but need hugh amount of php threads (imagine instances as 'windows browser' and thread as '1 windows with many tabs').
We don't need huge amount of MaxClient for event/worker but need huge amount of php threads (for php-fpm).