UE4 is only as resource heavy as you want it to be, just as Unity can be resource heavy if you follow certain patterns. Unity and UE4 and many others can achieve quite a bit of parity in performance nowadays. There are scenarios that either one has potential to win out in.
Epic has made great strides in so many areas that if you haven't tried it in a few releases(6ish months?), there is quite a bit of stuff that is better (both in cleanliness/precision but also in performance and overhead)
I just tried to open UE 4.14.2 (no scene) - it took 140seconds, how is that not resource heavy? Opening some basic project - 15 seconds. Making a small change in my plugin and compiling it ~2minutes. Intellisense are quite slow, VisualAssist even slower. Donwloading UE - several GBs.
I can recompile my whole engine in 20 seconds (and I am not using precompiled headers), editor launches in ~1 second, basic scene load ~1 second. Small change in source code - compile & link in 3 seconds. Intellisense brokes from time to time when using FBX SDK, but it's fine otherwise and without FBX SDK there is no problem. Engine size with some necessary data - a few tens of MB.
When I am doing something in my game and I have to change something, turn off engine + make change + compile it + start engine + load the scene = few seconds. It's so fast I did not even bother to implement hotreload for native code.
When I'm working on my UE plugin - the same cycle is several minutes.
the 140 seconds seems like something is wrong or some weird bottleneck is happening especially for a empty scene. I feel like opening a scene for me is about 10 seconds at most.
I thought you were talking about it being resource heavy relative to unity, not to your own home grown one, which is likely (and obviously) much lighter. I have no doubt in that comparison all the larger game engines have quite resource heavy editor. But the tradeoff is supposed to be that few extra seconds loading it up and few GB downloading it, saves you potentially months of work you don't need to do yourself in a more custom engine.
the 2 minute plugin change also seems really off. I can tweak my plugins and recompile in a few seconds.
Intellisense is much better than it used to, at least on my own machine, but I will admit it was finicky for me for a while. Its usually instant for me nowadays, though I will admit at one point it was ridiculously slow(5-10 seconds). I have no idea what I've changed and I am on the same computer.
no getting around UE4 being quite big, several GB, to download.
Epic has made great strides in so many areas that if you haven't tried it in a few releases(6ish months?), there is quite a bit of stuff that is better (both in cleanliness/precision but also in performance and overhead)