Is astrochronology a proper method?
Yes it is used and it works. I've heard varying viewpoints on it's accuracy and dependability though. I remember my earth science lecturers were in three camps with it:


one felt that the dates weren't consistently reliable, the data he'd gotten from astro-dating in the past had very poor independent confidence margins when there was no radiometric calibration. He implied that the results felt as though they had been pulled out of thin air.
two would gather testable material for future study but didn't use astro-dating themselves. It was an interesting but immature technique that might be useful in future but not to them.
only one felt that it was really, immediately useful.


Do note that this is in New Zealand, we're a geologically young and active country, so much so that we rarely need longer range radiometric testing like Uranium-Lead or even Potassium-Argon, we can Carbon date most of the sites we're interested in. Fine calibration of longer range datings is much less of an issue here than in older, more settled, locations.