I'm going to say this and then log off for a bit because I have a pickup shoot to prep.
On my current feature that I am producing (wrote it as well) our crew was paid fairly, above minimum wage requirements and in keeping with labor laws. Would I have liked to pay more up front? Yes. But we just didn't have that ability with our financing.
My fellow producers and I structured in bonuses for our crew should the film hit certain benchmarks. Should the film do well, they'll make way more money than they would making a standard union level salary for the same amount of time.
Every film is different, every financing deal is different, and so I don't think it is or should be mandatory for producers to set up deals like this.
What we paid people was fair, and if that's all they ever get paid, it won't be something I have on my conscience. There's a very good chance I never see a dime, since I deferred my writing and producing fee to make the project happen.
This is something I would never ask my crew, unless they begged to defer some of their pay in exchange for backend. I will always be open to that arrangement.
Indie producers especially are probably way more open-minded about structuring deals to allow more profit-participation. You aren't going to get that within the studio system, at least not any time soon.
So, BTL crew, please, advocate for yourself. Ask for a deal structure that will benefit you if the film does well. You'd be surprised what people will be willing to do!
If you fear your producer so much for asking for that, then maybe they're not a great person to work for. If you fear speaking up about onset work conditions that violate the law, then you definitely don't want to work for that producer again, and you should seek legal counsel to see how you can protect yourself and your fellow crew members, because if the producer is abusing or exploiting people they've likely done it before and will continue to do it unless someone steps up. Be the change you want to see in the world.
I'm not some heartless, bootlicking producer without a soul. I'm a writer. I'm a first AD. I'm a PA on my own film. I've worked harder than anyone else on my film (which is as it should be), and without compensation (also as it should be).
But to act like we, on the producing side, are stealing from crew by not giving out bonuses when not contractually obligated to do so really misses so much of the reality of paying for a movie to exist. Until you're in the driver seat, you don't really know.
Art directors risk nothing for their work. They get paid and they can move on to the next project. If the movie blows up they can leverage that massively or complain and make themselves a byword for industry insiders.
But the producers are the ones holding the massive bag if the movie bombs.
Is the art director going to surrender her salary if that happens? No.
Is the cast and crew willing to defer their fee in hope the movie does well? If so, let's have that conversation, but most wouldn't.
So why should they get an upside if the film does well? They don't deserve it, unless they negotiated for it and it is in their contract.
You can agree to the offered salary or not. But if you take it, and then the film makes a ton of money and then you complain about being exploited, you've shown your hand, and no one will want to play poker with you because they see how you operate.
Pay is a proxy for effort, but also risk. The risk you take as BTL crew is zero. The effort is compensated fairly (consent to the contract is agreement to fair, equitable trade).
But you don't deserve upside while also offloading all the downside to the producers.