I think it's 50/50, Briedis would be a heavyweight in any era besides the 90s and beyond and gave Usyk his hardest fight while giving Opetaia hell at 40 years of age. How would he fair against a prime heavyweight verison of Spinks ?
Briedis started as a heavy but couldn't get the fights. Anyway, I think a lot of Briedis, but I usually give the benefit of the doubt to the proven great, although I will say this is one that lacks data, since Briedis' career was a series of false starts.