> Do you know why it's a resource hog? Is it the nature of Ruby (that appears to be what they use) vs php, or is it because it tries to be an SPA that has no pagination?

Ruby dev for 15 years here. Ruby is definitely slow, but in 2022 it's "tens of milliseconds to answer an HTTP request" slow.

They chose a javascript framework that turned out to be outrageously slow.