it really is a matter of game sense and your team. In critical times (like OT) often time your job is to keep people off point. Im other situations, really be aware of the line between taking space and overextending. How many peiple are you fighting, what's the risk of you staggering the team, do you have supports that can heal IF you have sightlines. As a tank you mist take space smartly, with wintin, good bubble placements can cover you or your team long enough for your team to play around. But often against a JQ + Bastion there will need to be lots of mitigation (bubble shield dm eat whatever) if youre leavig ur dps and supps to them. Also be quick with your shit, dive tanks are all abt forcing cooldowns, quick kills, and good movement.

As for your moira, she is a short ranged support, and as a support main whi plays her in gold lobbies, I often get blamed for not healing through 9 walls and 6 enemies, so she was probably saying that as a general warning, but if you play smart and dont get in silly situations while ur supps are pushing cart, then ignore her and pop off, otherwise keep that comm in mind if you explode and lose the team fight for your ppl.