It appear you are trying to set a development environment up for Symfony.
A simpler solution would have been to just create the virtual host and tell it to not use the .htaccess as it is the .htaccess file that is causing your Virtual Host setup to get overridden.
Remember .htaccess gets applied after whatever you do in the httpd.conf or httpd-vhosts.conf files.
Virtual Host for development mysite.dev
<VirtualHost *:80>
ServerName mysite.dev
ServerAlias www.mysite.dev
DocumentRoot e:/testing/mysite/web
<Directory "e:/testing/mysite/web/">
// disable the .htaccess in the web folder
// from undoing the attempt to go straight to app_dev.php
AllowOverride None
Require local
// this forces app_dev.php to be run
<IfModule rewrite_module>
Options -MultiViews
RewriteEngine On
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^(.*)$ app_dev.php [QSA,L]
</IfModule>
</Directory>
ErrorLog "D:/wamp/logs/mysite.dev.apache.error.log"
CustomLog "D:/wamp/logs/mysite.dev.apache.access.log" combined
php_value error_log "D:/wamp/logs/mysite.dev.php.error.log"
</VirtualHost>
Virtual Host for testing in the PROD environment
<VirtualHost *:80>
ServerName mysite.dev
ServerAlias www.mysite.dev
DocumentRoot e:/testing/mysite/web
<Directory "e:/testing/mysite/web/">
AllowOverride All
Require local
</Directory>
ErrorLog "D:/wamp/logs/mysite.prod.apache.error.log"
CustomLog "D:/wamp/logs/mysite.prod.apache.access.log" combined
php_value error_log "D:/wamp/logs/mysite.prod.php.error.log"
</VirtualHost>
Now you can leave the .htaccess file as it is, as it may be very relevant when you come to move this site to a live server.
You also do not need to amend anything in the default httpd.conf file from the standard WAMPServer defaults.