Yes could have but would it have saved much time ? Again I could have used a lever valve, but the gate valve is free flowing and probably will never be turned off again, the salamander pump comes with isolating valves on the flexi connectors, just in case it needs removing.
It’s best to leave cylinder filled drain a pint of water then unscrew flange then drain 5 litres once cracked and then install a flange stops cracking the cylinder