Regardless of whether or not Gato is easy to beat, the creation of him at all is impressive...Perhaps the invention the people see as blowing up is something akin to her Disposable Explosion Blast Pistol (the weapon she uses to bust Crono out of jail)...All scientists have failures anyways, that's the core of the scientific method!
The Pendant's reaction is what caused it to appear, the Telepod is what opened it. Obviously they thought the Pendant was important (possibly even necessary to have a returning Gate appear), so Lucca says to hold on to it...Obviously it's not necessary to open the Gates because as you said, Lucca didn't have it and she opened the then preexisting Gate with just the Gate Key...