While your claim is true---big budget movies, etc., need someone to pay for them---the unspoken corollary you're implying isn't true---that without the current economic model, no-one would pay for big budget productions, or that undermining the current model via piracy will reduce the rate at which they are funded.

The current model is: massive corporate copyright-holders can purchase the right the profit from an artistic production. They pay for its production up front. Even though we have a technology that can costlessly copy these products and very cheaply distribute them to almost everyone who wants them, the copyright holders maximise their profits by a) crippling this capacity by spend considerable money, labor and human expertise on technologies that artificially limit copying, and b) use state-supported coercion (e.g., fines, lawsuits, police, etc), to punish individuals who would circumvent these crippling technologies. To be clear, these copyright holders still make massive profits, vastly beyond what any individual they are persecuting for copyright infringement could ever dream of. Their policing of piracy is to make even greater profits.

Even though this is how big artistic productions are funded today, it is not true that in the absence of this economic model, big artistic productions would not be funded. The demand for these products would still exist, and if there's one thing our society excels at, it's directing capital to meet demand.

Alternative models that could fund big artistic productions:

• a centralised fund we all contribute to in proportion to our means (e.g., progressive taxation), that pays artists in proportion to how much their product is consumed (like the Spotify model, but publically administered, like TV licences)
• many small scale investors rather than corporate monoliths (like Kickstarter), whose investments are recouped by a) privileged access to get product and b) the still highly profitable cinema and dvd markets whose constraints (physical premises/media) are not compatible with free copying.
• a legislated solution that protects copyright until artists are sufficiently recompensed and then allows free distribution.

These are just some examples of the many possible alternative models for funding large art projects and deciding who should profit from them and how much. However the details aren't nearly as important (many different models could work), as the ultimate driver: whether our actions/systems/laws enhance or undermine demand for the art.

Piracy does undermine the current (corrupt, exploitative, reprehensible) economic model but it also increases demand for the media it distributes more widely and equitably. It doesn't, as you imply, reduce the likelihood of big budget media existing in the future, it increases the likelihood of it existing in a more fair and equitable way, that harness our ability to freely copy rather than crippling it for the benefit of the ultra-wealthy copyright-buyers.