Normally, same element is better option. At first when you level up you can use some weapons of other elements while you lack good weapons of your element, but going after a pure grit is a primary goal.

Each weapons level is a 0.5% to attack or HP. SR have an 3% extra and SSR with ++ have an 6% extra. What do you mean with 200k? On a Burst? one attack? final total damage?