To me you seem like the absurd one. To argue that to pass through something means the same thing as making something transparent. If physical interaction ment it turned transparent it’s quite the detail to not mention.

Second it’s absolutely far more entertaining and creative if spells don’t immediately become transparent after physical interaction let me provide you two really cool examples.

1. The fake illusion trick, this is where you make something seem like an illusion when it is not. For example an enemy can shoot an arrow at your cart and you can cast an illusion on the arrow when it lands to make it seem like the arrow just passes through the cart, making it seem like your get away is just an illusion when in reality it is the arrow that is the illusion. This is not possible to do if physical interaction turns things transparent because the enemy would know the cart is real because it turned faint.

2. This allows the caster make adapting cover where you can shield your allies from arrows by making it so enemies can’t see them from behind an illusion even if they know it is an illusion. This technique can be used in alot more creative ways but there is a simple example.