If you just go with Radions alone it will take a few to do a SPS tank. Kessil's are fine for soft corals or LPS but just do not have the punch to do SPS well alone.
Both lights benfit from adding T5's to the mix.
Don't know where this information originates but it's not at all accurate. I ran (2) of the 360 Tuna Blues alone over a 40 breeder I used as a frag tank and grew acros with NO supplemental lighting and this was with them mounted 24" above the water surface. The new full spectrum 360s should be even better. I now run (3) AP 700s over a 30" deep tank and am growing acros as well as an assortment of other sps corals very nicely, again no supplemental lighting. Measuring PAR with an Apogee MQ-510, getting 550-600 at 6" deep and 250 + at 22" deep, growing acros at both elevations. Lights are set at 65% peak intensity and hang 12" above the water surface (of course the further from center the lower the par which is true of all light sources). Kessils are definitely more set it and forget it. Set the timing for on/off/ramp, color and intensity at each set point and that's it. Set as many points as you care to program in.
I have never used Radions but have a friend that uses the Gen 4's and has an awesome looking tank. Lots of acros, all growing very nicely as well. He does utilize t5s to supplement but I believe more by choice than necessity.
Based on the results we both have had with these (2) different lights, I'd say you can't go wrong with either. Choose based on looks, price, whatever floats your boat, but both will get the job done equally well.
It seems to me that we tend to lean towards what we have the most experience with. Very few people have the opportunity (or funds) to have used every option available (Dana maybe comes closest). If I were to get into a new build I'd be looking at both of these myself, maybe even a few more that have come on the
market recently. Fact is I'd probably buy Kessils again because I'm happy with the results they've provided to date.