I’m not an expert. In my understanding you aren’t really contributing to decentralization unless you are mining. Running a node is more about not relying on a 3rd party and also helps with privacy. You’re also distributing another copy of every transaction which adds to decentralization as well.

All that to say, I’m no expert but I think there are degrees to which one aids decentralization and running a node is at minimum a step in that direction. But my understanding is that for more decentralization we need that in the block creation and mining more than on the node side.