The main factor holding LEDs back is their high costs. Those COBs aren't very efficient. A one watt diode puts out more than twice the light per watt as any COB. 1W diode=236 lumen/watt.......50W Cree COB=86lumen/watt They're just a lot easier for a do-it-yourselfer to build.
1W LEDs are no longer in the running, the most efficient small LEDs available to us are "10W" the Cree XML2 and the Vero 10 (a small COB). The highest XML2 bin currently available in warm white is T4 and it creates 126 lumen/W running at 25% power. The Vero 10 3000K creates 125 lumens/W at 25% power.
As for COBs, the highest CXA3070 3000K bin currently available is Z2. It creates 140lumens/W at 25% power cost about the same/ PAR W as the XML2 and Vero10.
The the CXA3070 top bins GG and I were lucky enough to score when they were available, create 161 lumens/W at 20% power and cost 20% less than the others mentioned.
There are no LEDs that can reach 236lm/W. The closest we can get is with the Cree CXA3590 5000K CD bin running at 300mA (13% power), about 197lumens/W. Speaking of those, thnx to a RIUpper I will be installing one tonight to test for vegging use