Define “true” and “valid” in this context.
The group of doctors did not, themselves, suffer damage from the passage of the bill, which at the time the suit was brought did not affect them. The perceived or forecast effects did not harm them. It claimed that, if passed, as passed, the bill would have this and that affect which the docs group characterized as “harmful”. Their position was one of theoretical advocacy.
That means they themselves did not suffer those ill results. That means they do not/did not have standing in the legal sense.