Well, as i understood it has failed because it could no longer provide the main benefit over B-52 it was initially intended to provide: high-altitude penetration - over it's development time, engagement envelope of SAM systems expanded in altitude and speed so much that even XB-70 could no longer hope to get through. So it wasn't any better than B-52, except much pricier. It could also get to the target faster, but for applications where time of flight was critical, nothing could beat an ICBM anyway. They switched to cruise missiles - to keep B-52s out of harm's way, and low-altitude penetration (B-1B), then when radars became capable of discerning things vs ground reflections too well, they switched to stealth - but Soviet Union fell apart before they knew if it could work or not.

So it's not about any technical failures of XB-70 itself, just that it turned out to be unable to do the job it was planned for.

Wrong?