They could lose 30% of their active power and still be commonly built. They're very powerful. But even then I think these items that grant aoe reactive defense will be popular support buys so long as they aren't junk.
I think their gold costs should go up a noteable amount if anything and be the extra luxurious support items with the less sought after support items being lower costs. But at the same power supports may just continue to save up for them though and just have them slower...
Current costs
2100g
2200g
2100g
2300g
2100g
2250g
2300g
2200g
Locket is miles away by far the most overpowered one as it grants instantaneous large shield. Sometimes I build it as a normal tank item. Or on fed Teemo as an FU to AP dmg. And still works as general defense/bait. For 2200g it gives 30 armor, 60 mr and a shield 300-600 large in size (consider it hp). A 30 armor, 60mr, 300-600 hp item is absolutely bonkers for 2200g. If locket wasn't bonkers bursting through before redemption procs which I think is a bit overrated yet solid item can happen more.
Locket should be weaker. Locket and redemption should be more toward 2500g
Like Riot literally made locket the most overpowered item ever, more than the old one and locket should be getting all the flak tbh
The real question is why would supports still save up for and buy locket/redemption even if they cost 20% more and were nerfed..? Why can't we get those damage supports items relevant..? I think it's because carries are soo squishy that their baseline survivability requires these items in a competitive game no matter how much you nerf them into unfun to own land (unless they simply became not worth the buy)