This is a gacha game, you never know what you'll get. So the most optimal route would be to level every element and get everything valuable event related. There are plenty of examples throughout the forum of people asking for help with their so called main teams only to find out their rosters contains units that would make a better team of another element and those people posting them drawing a SSR not of their main element.

There's also fact that the strengthening curve exists, as in it becomes much slower to get stronger the further you get into leveling your team's grid. Any high rank player can tell you how steep this curve is while trying to break that 50k power for a single element. Because of this curve, the amount of time and effort one could put into getting a single team to 50k atk, another player could probably make 6 different element teams of 35~40k.