Don't blame Plesk.
Your problem really isn't revolving around some deficiency of Plesk. In fact, Plesk and the wonderful Filemanager system makes installing Joomla a breeze.
Chmodding the folders to 0777 is actually pretty easy, and is only required to install Joomla. Once Joomla is installed it's possible to set most of those folders back to 0644 or some other more secure setting.
Personally I leave the folders at 0777, because of the security built into Joomla, there's a slim chance that those folders could be exploited.
Granted, it's not the most secure situation, but I've used other scripts that are no where near as secure and thanks to XMLRPC (which isn't in Joomla), those scripts are very exploitable.
I've had no problems running Joomla on nearly all of my sites even leaving the folders set to 0777.
Yes, I know it's possible to exploit a folder on a site set to 0777, but it's not easy and there's not that much that can be done with it.
I wouldn't blame plesk, because you are afraid of setting your folders to 0777. You can always set them to 0777, install Joomla, and then change them back. However you could break Joomla by setting the permissions too low.