I wonder if he's actually capable of that. He might just exhaust his haki very quickly by overextending. I honestly believe Cracker's biscuits are only stronger than steel because he is there to imbue his creations with his powerful armament haki. Similar to how Katakuri's donut punches still retain his haki when the arms are floating in midair. He actively protects them with haki the moment they are created. When Cracker is not around, his creations turn to regular biscuit.
Pedro and Brook being able to casually slice up a biscuit and sneak inside the thing doesn't make sense otherwise. Why would these soldiers be weaker than the regulars clones? Cracker spammed his tough clones for many hours against Luffy. If this is about Cracker maintaining his secret identity, he should easily be able to change the appearance of these soldiers so they don't look like him while keeping the extreme toughness of the biscuit.
Also, you would figure that Big Mom could replace all of her tens of thousands of chess soldiers with an army stronger than Pacifista remotely powered by souls like the Sweet City soldiers. Maybe not all of them, since they are weak to water. But at least groups like the Enraged Army or the army that invaded the Germa Kingdom should have been 50% biscuit soldiers. Again, if Cracker cares about his secret identity so much, he could easily change the army's appearance as a master artisan.
But Big Mom doesn't do this. She wants an army of giants instead of an army of Cracker's biscuits soldiers. Why? The only reason that makes sense is that without Cracker's haki protecting his creations, his biscuits are only tougher than average but nothing special that can only be broken by Gear 4th. The Bis Bis fruit is amazing because Cracker has powerful armament haki to combine with his constructs, give to somebody like Mr. 3 and the power only slightly improves his current standing.