Using `age` or `rage` is deadly easy. Also, e2e is most effective when it happens out of band - if the idea is "I don't trust Dropbox, so I want client side encryption" then you shouldn't trust them to do the e2e anyways. I realize it can be more complex, but managing it yourself gives you the maximal benefits of e2e.
It's not just "better", it's the only approach that addresses the real threat model. So you can go with something simpler like checking a box but then you aren't getting the same feature.
FWIW this is the reason, to my understanding, that Dropbox has always been reluctant to support this feature - because if you actually want E2E you probably want it out of band.