Try not to worry too much about the zealots backlash. Ne thinks I'm attacking a worldview instead of just pointing out factually incorrect information.
It's true that 70MB is very small for games, especially if you're talking about something with 3D contexts and meshes. But it is also true that most mobile games could be built with Javascript and still be just as performant and served as Progressive Web Apps in less than an MB. So, in the frame of reference, 70MB is gargantuan. I certainly understand why OP took offense, because their frame of reference isn't "all games", it's "games that focus on these very specific metrics I care about".
If that's your only criteria, then obviously Unreal would be bad because it doesn't optimize ONLY for size, it optimizes for a bunch of other stuff, and leaves a lot of optimization on the table for devs to do on their own. Of course, all of that is true of Unity too, which is why you can get smaller package sizes (20MB is not impossible for Unreal, but it's easier with Unity), but you still can't come even close to something that is "efficiently" packaged. For that, you'd need to move into lower level stuff like engines and frameworks in Rust or C++. Eschew the niceties of the IDE and really get that package size down to zero!
Of course, that's not feasible for a lot of people, so (as always) you're talking about what kinds of things you're trying to optimize for. And Unreal produces package sizes well within the range of acceptability for even Unity games. Most of those are at least 200MB+. So it's a petty complaint made from a place of self-interest, that is only true in contrived instances, which seemed worth pointing out.
As a stray aside, though: I have had games developed in both Unreal and Unity on the play and app stores and no one ever said anything about performance on either of them, so I really don't know what kind of devving OP is talking about that results in such poor performance. I can't imagine I'm doing anything uncommon, so I'm very curious as to what the hang ups are, mainly in a "are you sure you're doing this the Unreal way, instead of trying to force the Unity way in Unreal?" kind of way.