Those items are already pretty weak in terms of base stats, if you nerf them then they really be a waste of an item slot especially on tank supports *who are already getting shredded and deleted
It really isnt the case of aegis and redemption being so strong, its other items being too weak and unable to contribute to the team very much, even the much more selfish items (like knights vow) dont provide enough for the sake of them being selfish versions of support items, their also needs to be more items available to a support....maybe even a strict support item that requires you to have sight stone first but increases your max cdr cap by like 10-20% along with giving 10%