First, I am not saying that one light is overall better for every situation. It depends on the tank dimensions, aquascape, corals being kept and the reefkeeper.
If you are happy with Radions, Kessils, T5, halide, orphek, reefbreeder, etc.... I am happy for you. That is great. My comments are with respect to my experience, on my tank, on the types of corals that I like.
An XR30 or SKY likely has very similar integrated par. That is if you sum all of the light going into the tank, it is likely very similar. I also would not be surprised if the same is true for an A500x. They simply have a different distribution (also there is a slight difference in the color output. All will grow coral well, but each may be a closer color match to your personal taste)
If you are par limited, I agree. 3 will not replace 5. If the 5 XR30 are not being run at max, rather they are at 60%, then I could see replacing 5 XR30 @ 60% with 3 SKY @ 100%. Note that this is often the case in the BRS reviews. Ex. 3 XR30 over a 48" tank where 2 SKY could easily cover that.
In a frag tank, I would agree. I try to use aquascaping and coral shape/size/ character to create par and flow zones.
Totally agree. With LED's you have to be careful with direct illumination. On one hand, the intensity has to be high enough to bounce off the glass/ rock and get to the underside of corals, but at the same time not cook the top. Before running the SKY, I was running 2 A360x and 4 Reefbrites. One of my motivations was also just to simplify. Here is a comparison of my setups:
2x A360x (40% int, 30% color), 2 RB XHO Actinic, 1 RB XHO 50/50 -----> ~200W
SKY in Sky mode, 100% intensity (90% overall intensity) -----> ~200W
I am really glad that there are so many good choices in the market. There will always be little things that can picked on about this or that, but overall choice is good.