Shields aren't meant to do either of those things. If you terraform them correctly, you can use them to stop bombers though.

If you have a major economic advantage, you can use shields to stop artillery fire. It doesn't make you invincible though. If you want to build an effective troll-base in the center of the map, you need to use much more terraform. If you wanted to win, just place a few Impalers in mid.

Building a nuke at the front is something you shouldn't do unless you want to ridicule your enemy.

Do you have an idea on how this could be improved upon?

Either way, the main point that seems to have been lost is: "To beat something, kill it before it kills you." Which applies to pretty much anything in zero-k, including economy. Even shields are mainly geared towards offensive use where they can temporarily block enemy fire while dishing out damage themselves. They will not counter any unit in a way that doesn't kill it. How could we make it clear that this is their purpose?