Very unlikely it was Roberts, exponentially more likely it was someone other than Roberts.
1.) Roberts has shown on multiple occasions that he can be influenced by the political implications of court rulings. He’s a baby splitter. Even in his opinion in Dobbs he tried to give a little to the pro abortion side as he gave a little to Mississippi. His opinion for the ACA mostly read like a dissent, strongly suggesting a switch in his vote. This is more a setup to the next point, but on its own, he would be unlikely to leak because the leak significantly impacted the reputation of the court that he so jealously guards.
2.) If he were the leaker, by handing over (or through an intermediary) the documents to a left leaning reporter, he would be guaranteeing that the reporter would have big leverage over him, for the rest of his career. It would gain him nothing, and now he would be subject to blackmail and impeachment for the rest of his days. With a dem majority in the senate and house, Roberts would most certainly be impeached if he were revealed as the leaker, and the GOP just may be dumb enough to go along with it to see to his removal and the remaking of the court.
3.) Two other clerks for leftist justices have already been shown to be outspoken abortion zealots, and have connections, either through mutual friends, prior work, or as sources for the lefty reporter. There was also a recently appointed Justice in waiting who has a current clerk staff and would possibly be getting some courtesy copies of predecisional drafts in her possession. Her staff may or may not be coming along with her to the USSC, and may also not be as guarded about the sanctity of the Court.
3b.) Further to the other point, A right-leaning chief justice using a leftist reporter who hangs in the same circles as recent law school grads as a pass through for a leak is like a college graduate buying cigarettes for teenagers because he is looking for social acceptance.
4.) Finally, leak investigations frequently find the leaker. Probably it’s almost always. The reason you rarely hear about the identities is that the investigations are not for you, they are for the government. Watch where the clerks end up next year for big clues, there are relatively predictable career paths for USSC clerks, and if someone suddenly has a strange deviation, that’s probably your guy (or gal... I’m not a biologist).
Thanks jz. Those points make a lot of sense.