you do NOT need to download custom packs. the sv_pure command is only relevant for mapfiles that you MUST have and the game loads for the map.
My propose is to install the ET ultimate Installer: http://etui.kashu.fr/ eventhough it was created quite a while ago it still hast most custom maps and at least the latest version of etpro. When you now disable downloads you should be able to play on most etpro public servers. Though there is a new anticheat called TZAC, which some publics may use by now. Its a third party tool from which you have to start your ET. It is mostly used for clanwars, but some publics “might” have it aswell.
