Sure. Before you go further with your argument, let me tell you about the posters in my living room

They are behind glass windows in frames. My intended function for these glass windows is to keep the posters flat and in good condition, as well as being esthetic. Nothing about any blocking of the flow of air.
Similarly, there are some trains at my company where the company intends for them to have the function of providing spare parts. Nothing in their intended function about riding around on tracks bringing passengers around - even though that is what you might erroneously have deduced from looking at their design and engineering.
There is no such thing as an objectively determinable purpose. You can objectively determine that an object can have a function, the train can have the function of riding around on tracks, it can also have the function of providing spare parts, both of these can be objectively determined. What you can't determine is which function is its
intended function (ie its "purpose") - that just depends on who you ask.
You're moving from a circular argument based on giving special consideration to the intention of the person you call the "owner" to giving special consideration to the intention of the person you call the "designer" or "engineer". It won't help your argument though.