The first is definitely something that would be good to have, probably even outside of combat.
Devs have already talked about other shapes for 4x tiles and decided not to change it.
Poison has already been nerfed multiple times. Honestly, I think players are just not aware of the ways to counter it.
Guard gems are very good if you have a TEC advantage. They're not that broken otherwise, since you usually aren't dealing any damage while guarding and are still taking some.