TL;DR
Make Tank Cannon Shells gain increase to piercing power from physical projectile damage technology, so these shells will be viable at least in some scenarios.What ?
Simply make piercing power increase to the same percent as physical damage. However such improvement shall not be applied to explosive shells, as they are meant to detonate on impact.Why ?
No one uses piecing cannon shells, they are able to piece up to medium biters and big spitters, but explosive shells are also great at it, but if they hit thicker enemies the shell will get stuck and will do miserable damage compared to area damage of explosive shell.They cannot even pierce the nests. And at the point where you get the tank you will expect soon big biters, which make piercing rounds totally useless in combat situations.