@Meddler: Is restoring an ally's mana considered toxic?

When Soraka got reworked, she lost the ability to give mana to a teammate. And a long time ago, we had Mana Manipulator and Shard of True Ice, which were support items that let you get a weak mana regeneration aura, but those were removed because of certain lane compositions (i.e. Sona/Ezreal). Ever since those times, the only way to restore an ally's mana is to use Clarity, which is simply not viable because of the requirement for Exhaust.

Then, a few months ago, dataminers found files on the PBE for new mana items that included effects that could restore allied mana. But those were quickly deleted and never seen again.

Is the very concept of "restore an ally's resource" toxic gameplay? If not, can you share with us why there's no viable way to restore allied mana right now?