Reminder buying Relic Shield doesn't really mean a champion has sustain
That's like complaining that Renekton has AoE autos because he can buy a Hydra, or that Malphite takes less damage from crits because he can buy Randuin's. The item has sustain, not the champion. If the option to buy Relic Shield was sustain, than every single melee support has sustain and therefore should be dismissed completely when comparing two melee supports.
Besides, Relic Shield sustain is nothing when compared to a champion that actually has healing in their kit. 40hp every minute is negligible compared to 60hp every 10 seconds (albeit at the cost of a bit of mana).