Ajax requests in Drupal 7 like in WordPress, is it possible?

Question

Drupal

Trite, but yes, is it possible to build your ajax requests in drupal in the likeness of wordpress, but with a handler function in template.php? Standard tools like Drupal.ajax do not suit.
For example, in wp it is done like this:
ajax

$.ajax({
  url: ajaxurl, // ссылка обрабатываемая ajax запрос ../wp-admin/admin-ajax.php
  data: {
    'action': 'addreview', // action - действие к которому позднее прикрутиться хук/функция обработчик
    'form_data': form_data, // какие-то данные
  }, 
  type: 'post',
  dataType: 'json',
  success:function(json){} // результат
});

handler in functions.php

function clinic_add_rewiew_form(){
  // $_POST['form_data'] Что-то обрабатывает 
  die();
}
add_action('wp_ajax_addreview', 'clinic_add_rewiew_form'); // регистрирует функцию обработчик
// add_action('wp_ajax_($action)', function_name());

And actually, can I make a similar ajax request and put a similar hook handler in the template.php file of my theme and actually call Drupal core classes or module hooks in the handler.
One of the reasons why I need this is the reluctance to connect Drupal scripts, of which there are a lot and they only slow down the site, I like it when it is clean and only what is necessary on the site is used, the second is that before sending some data to the site, I need to carry out some manipulations that cannot be implemented by conventional means, if you forget about the first reason.