I don't think that's quite true yet. While I vastly prefer UE4 to Unity (and would recommend UE4 in most cases), it would be a mistake to underestimate the value of the huge amount of paid and free content that exists for Unity. Furthermore, UE4 gives the option of Blueprints (which many find insufficient or clumsy) or C++ (which can be very intimidating). UnityScript/C#/Boo sit between the two, making it preferable for those who want to write actual code, but don't want to deal with C. Furthermore, UE4 is still very developing expected features. Until 4.8, you couldn't do SSR on translucents, couldn't do graphics profiling on OS X, and couldn't switch splinesmeshes from being open to closed without corrupting your maps, etc. I love UE4, but it's still got a lot of ground to cover.
You're absolutely right about the content and tutorials available for Unity, that's a humongous boon. But that's a gap that will rapidly close, especially after UE4 dropped the subscriptions.
I was very wary of Blueprints, but after playing a bit and seeing just how they work, I was sold. Same with using C++ natively; it seems daunting, but you're calling the same methods your Blueprints do, it's almost drop-in easy.
Definitely it's gonna need to make some progress, but the gap is closing.
If you're just doing 2D, it's really bloated and clunky. The UI stuff isn't great either.
I imagine this will gradually improve, but for now it's really not an appropriate engine for that class of games. Anything from LÖVE to Unity works much better.
For UI you really should check out BLUi. It's free and beats the commercial offering from Coherent in our experience.
We got some pretty complicated HTML/JS/CSS up and running and nicely integrated (js talking to blueprints and vice-versa) in under 30mins. It's fully backed by Epic now through a grant.
It handles video and audio nicely as well. There's little reason to consider using the inbuilt UI stuff when it's so easy to leverage existing HTML skills to build it out.
Grid is suppose to be a lightweight engine solution on top of LÖVE as it's framework. I feel that Unity is comparable to UE4 as far as 2D games go: overkill. LÖVE doesn't solve any boilerplate issues for you, and you end up reinventing the wheel.
A few of us from the Valve development community, EA, and Blizzard wrote this as a side project.
Yes to Macs. Cross-platform is something we'd like to work out, but we end up pestering the LÖVE team to implement underlying framework changes.
LÖVE's team moves really slowly though, and we release updates on about a weekly basis. We'd eventually like to move off of them but keep a similar framework API for people to migrate away from.