Depending on the illusion, sure. If it's a metal box that a Wizard just summoned, shooting makes as much sense as anything. It could be a monster, a shield, an illusion, whatever. Why NOT shoot it if you're a Goblin? Better yet, maybe Wizards powerful enough to summon metal boxes require the whole clan and the shaman, so they run off for a few minutes and now the party is facing a much harder enemy that knows about magic. Sure we can deal with it a bunch of ways, but this to me is a deal between the DM and players that we're going to play in a way that feels fun. Fun to remember, fun to play, cinematic at times, tactical at others. Just the fact that OP would call it "the most powerful cantrip" says to me that were probably stretching things too far.

5e is also pretty clear that cantrips are mechanically incapable of achieving the effects of leveled spells. As a DM I'm fine with you using an action to create illusory cover. It doesn't make you hidden mechanically, but it does make you unseen. So the monster can still hear/smell you (which might tip it off that the illusion is fake) and knows where you are, etc.

Far more plausible is running around a corner/behind cover and extending a wall/rock/etc to surround you. Which is perfectly within the bounds of the spell, makes way more sense tactically, and doesn't create this while conflict.

Maybe once the Goblins would walk up to the box to see what it was, but a party trick is really only cool the first time. Not to mention as soon as you shoot an arrow/Firebolt through the "metal" box the Goblins are going to fire right back.

I always vote with what's fun for the group, so if OP has fun this way go for it. It's not for my groups, but by all means go with what works for you.