I had this exact same problem where I became entirely disillusioned with the output of my work after having become reasonably senior and realising that the majority of my time and effort ammounted to projects which either failed or treaded water. The unfortunate reality in business is that the projects that truly change the world are 1 in 100. They don't look or feel much different from any other at the begining but when traction really does start to take off you know you have something right. I think from your description, you need to work at a startup where you have genuine impact. This is the only way you truly "feel" meaning. You might still build something that's reasonably worthless to humanity, but you will do it your way and take your own risks.