UE4 has high minimum requirements. And yes, the package size is definitely annoying when the leading competing engine for mobile can crank out apps a 3rd of the size easily.
Basically just decide what you want your minimum spec device to be. At the very lowest end, you will have to go for unlit materials.
LGL15G (or something like that) - dual core processor and I think adreno 302. 512mb ram. $20-30 phone you can buy at a grocery store (I bought this last year). It can handle 16 rotating objects which have specular / roughness whatever set. Not complete mobile HDR (I don’t think) but not unlit material. On top of that some background scenery that is unlit. Runs at around 40 FPS.
I have a Moto G 1st gen which benchmarks about twice as fast as the above, which is something like 3 years old at this point and was mid range then. Runs the same scene except with 48 rotating objects with lighting and it keeps 60fps. Didn’t bother trying to go higher, because that’s as far as my game will go.
I also have a Moto G 4th gen which is a mid range phone from 2016. I haven’t really done any benchmarks, but it blows the other two out of the water. And you can get this phone easily for < $200.
In my case I’ve just decided that the Moto G 1st gen is going to be my minimum spec device. There has to come a point where you say “I want at least this much performance with these visuals”. You don’t need to develop for every phone in the world. And phone performance is just getting better. Maybe if you’re targeting more developing countries you’ll have to be more wary of performance. As it is in the US, most people get a new phone every 1-2 years.
Anyway for sure UE4 is not a lightweight engine. My point is that it’s possible to create games which still run on relatively low performing devices. I mean, compare the specs and benchmarks of my target Moto G 1st gen to the newest iPhone or Samsung Galaxy. UE4 has high requirements for the GPU where other engines might be lighter. It’s just due to how it’s designed. UE4 can give better visual quality, but the cost is it has higher system requirements.
Even for seemingly simple scenes like dynamic lighting without shadows, Unity does much better on low devices. I’m talking a 2012 Nexus tablet. You’d be hardpressed to get 20 dynamically lit objects on the screen at once and keep above 20 fps. Meanwhile the same thing with Unity’s lighter rendering it can hit vsync of 60fps with ease. But really, look at the lighting differences in what you can achieve between the two on mobile and what the minimum you want to support is. I was originally mad UE4 didn’t really perform well on that 2012 tablet but at this point, who even uses it? I don’t. Even my Moto G1 is really slow nowadays.