Well, in a way that is correct- if one is thinking only about delivering a nuclear weapon....
On the other hand, being able to zip over unfriendly territory at will, unhindered by AD of any sort, to snap a photo/image of a critical site ( unlike most SAT sensors even today- they zoom around a predetermined orbit, needing NCA authorization to change position) in the here and now was invaluable.
Finally, having the technology ability and will to use such a platform was a tremendous asset to the cold war effort on the part of the US and NATO.
The Russians tout the hypersonic missiles they claim to have/had (oops they blew up the whole facility) while we are keeping such stuff rather quiet.
Some dogs don’t hunt.
The Russians knew nuclear ramjet since 1950s, just like regular ramjet. This technology is being revived not for the reason they are behind in technology.