The person running a node is part of controlling the bitcoin system. If you use a wallet from a third-party service, or an address given to you by the market, then you have no control over the system. You can only say that it is one of the users of this system.
There is also a saying that the miners control the entire system, but I think that the miners are producers and have a great influence on the system, but they cannot say that they completely control the system.