Batman becomes a Super Saiyan

Mxy decides to endow Batman with Goku powers and puts him in a room where time is at a halt so that he can train for a year with those powers. He starts off at Frieza saga Super Saiyan levels and is given a full history on how Goku powers work and what Goku has achieved over his time since meeting Zeno.

Once the year is over, would Batman be an elite on the JLA and would he stay on the team or quit and become a solo hero?

He already is an elite superhero of the JLA... and that's without any superpowers.

As a SSJ, he could solo JLA even easier than when he had Superman's powers.

I can't even imagine the Bat-haxx x50.

Batman with the powers of a Saiyan would not be elite in DC or Marvel. Saiyans don't have the physical stats of elite heralds. Saiyans are all about KI. KI output and KI absorption. When it comes to physicals, they are very low on the power scale.

You can make all the arguments in the world for Muten Roshis moon busting ability, but even a theoretically much, much, much powerful Goku was struggling with "only" 40 tons. He had to Saiyan out to deal with it.
Wasn't Super Saiyan Vegeta struggling with 1000 tons?

I was always under the impression that a punch from Superman would make Gokus head explode due to how quickly Saiyans take damage from punches compared to "galaxy busting beams" (LOL).

Carver where the frack have you been??? Bruce is ALREADY a Super Saiyan. In fact he has already mastered ultra instinct many times.