Per the link below, mobile web is anywhere from 15 to 60% of mobile traffic. Reddit isn't listed, and it's 4 years old, so who knows, but I'd imagine it falls somewhere in the same range, probably closer to the lower end?
https://www.statista.com/statistics/1019768/us-retailers-app...
The app sucks.
I try to use mobile websites instead of apps because I feel like the tracking data a company can get from a web browser is less granular than app tracking data.
Apparently all five of them use my little web browser extension with Reddit-specific features, requested by users.
But I can guarantee that your estimate is totally wrong.