Appears you're correct.
Treatments for powdery mildew must be applied at the first hint of disease.
Harvest the pink tomato and let it ripen on the counter.
Then open up that area as much as possible to increase air circulation.
Water at ground level.
Remove the brown portions of the leaves because thy won't ever re-green and, right now, they are limiting air circulation within the plant.

Here's the plant after trimming the affected parts. It has one branch of leaves left! The remaining leaves show a hint of powdery mildew too...

You did a good clean up job. There aren't many leaves left to support the growth of that much fruit, so you may want to pick the ones that are showing a bit of color. You can use copper spray on the good leaves to keep the mildew at bay. Hotter drier weather will help, too.