It's true for reddit, with its autoloading of videos, but is it the same for lemmy? The browser version already shows you the least amount of possible data, what more could you optimise?
I think a lot of it has to do with the constant updating bug. I burned through 50gb's of data in a few days using the webpage, where the apps sip data. I really wish Android had a "hey, something is burning!" for data usage like that..