[D] Is UK PhD as good as US one?

Despite equally great univs in machine learning in both UK (also include Europe) and US, the PhD duration differs a lot (UK typically 3-4 years while US typically 6). Is UK PhD less valued in the ml community than US? I do believe that there is more coursework in the initial years in US than UK, but is that the only difference. If both are equally good then why don't people opt more for UK PhDs?

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