Those things are not as coupled as you make them sound: the vast majority of people getting paid interest on their ETH won't be running a node. They'll be receiving interest passed on by exchanges or other centralised entities that are staking their ETH.
And if those entities give them some kind of token they can trade around, giving them rights to their deposit plus some profits, that token might well be a security.
But if I loan you dollars and you promise to do something profitable and give me more dollars back, that doesn't make the dollar a security.