I remember a long time ago reading that the Gold/Silver meta had Hidden Power banned on Raikou and Zapdos, however, I cannot find any resources as to how different the meta was changed beyond Ampharos having a larger presence in the meta before HP was unbanned. How much of an impact would be made on OU if Hidden Power were banned on them again today? What Pokemon were higher or lower in usage during the HP ban?
It is hard to compare because people don't play the game in the same way, people have a much better knowledge of the metagame and the mentality has changed a lot, but that's normal because at the peak of GSC in Netbattle (with HP legends banned) GSC was around 7 years old. The 20th anniversary of Gold and Silver games in Japan was 2 days ago, and in those 20 years the community knows a lot more and the metagame has been developed a lot more.
MrE gave a very good example in Blissey, and how its usage was much bigger before the HP legends ban when Blissey would prefer facing a HP Zapdos rather a Drill Peck Zapdos. If we were judging metagame changes based only on HP Zapdos being allowed, Blissey usage would have increased, when the reality says Blissey usage has dropped a lot over the years.
And now to answer your question about what the metagame would look like if we banned HP legends again, and this is purely theorical, I think that Zapdos usage would drop a lot, and the usage of grounds would rise a lot, especially Marowak and Nidoking. We would start seeing more defensive teams with BDLax + SD Marowak + Heal Bell, or with Nidoking, since both Nidoking and Marowak can now completely wall electrics. That would also mean that explosion teams in general would probably be less effective. Raikou would miss HP, but Crunch is still a very good attack that can still hit Egg hard and can get some key Sp Def drops and would still have a big usage in defensive teams, although it would have a lower usage since some of the stalls would be replacing the Raikou with a ground like Marowak to have a greater breaking potential.