I think Sigma’s works like this? it does have a cap, I think? if not, Zarya’s bubbles definitely do!
I think that the removed shield generator from sym can be repurposed for a tank character, after all physical shields and regular shields are very much so a defensive skill, of course a few tweaks would be needed, I would like it if it was a temporary thing and if it was centered on the character itself so that he could move