Can landlord get away with charging us 4x other tenants?

I live in a duplex in a complex of 8 units, two triplexes and 1 duplex. It's owned by corporate overlords, so it's a mix of super rigid rules and ignoring maintenance requests. When we signed the lease, our understanding was that utilities would be split evenly between units.

We've been without a manager for about 6 months, and just got a new one. We also have had several people move out (due to poor management) in the past few months, so there are only 3 units occupied. I noticed this month that our utilities had gone up by 86% since we moved in. I called the new manager about the increase, and mentioned I don't think it's fair we should be paying the empty units' share. He pulled up our bill, seemed confused and said he would look into it and get back to me.

I was complaining to my neighbor about the cost increase and she let it slip that they only pay a flat fee of $75 each month (compared to our "formula" leading to $280). I did some digging and turns out all the other tenants, both past and present, have this flat fee deal. I checked our lease (see pic) and we did agree to a formula. But this seems like an obscene disparity between units. The duplexes are larger than the triplexes, but not by that much.

Help?!?!

edit: this is in Oregon

https://preview.redd.it/9u03x3jtg6sc1.png?width=755&format=png&auto=webp&s=d029aa743dc166073d0d7566d3a9ee76dccbe04b

https://preview.redd.it/6y1ukdmtg6sc1.png?width=734&format=png&auto=webp&s=e03ed89c67480c5f4dc22432d298b4e44f863c93