The petition is only one part of the puzzle.

Keep Android Open also says to contact your regulators and fill out Google's developer verification survey, both of which either directly affect Google by influencing internal processes, or put regulatory pressure on them to back off.

The Change.org petition is moreso just a way to count overall total supporters, and add one more lever of pressure that can be leveled against them. (e.g. instead of "we've had a lot of people contact regulators" it's "218,000 people are actively taking the time to tell you they don't like this", can be cited by lawmakers, advocacy groups, etc)

That said though, I do agree that a change.org petition on its own is... generally ineffective most of the time.