Your spend built all of it. Each partner, each platform, and each tool vendor wrote their contracts rationally, to protect their own IP and their own operating model. None of it was unreasonable. The aggregate is what is expensive. When you look for what survives the transition intact, you are looking at a list assembled from the terms of six separate agreements, none of which were written with the others in view.
The reset begins. Baselines, models, and attribution logic must be reconstructed, at cost and on a slower clock than the one your competitors are running.
This is not the result of poor decisions. It is the structural outcome of a vendor model that was never designed around portability.