The higher Color Rendering Index COBS have more complex phosphors. You need a more even spectrum to get good Color Rendering. Narrow blue plus narrow yellow may look white to us, but a better phosphor mix has all those in between wavelengths and makes a lot of different colors look like they would under bright sunlight. That’s a high CRI score. They may also hit some absorption wavelength in the plants.
The real problem with colored LEDs is they each have one wavelength in a very narrow band. That collection of narrow bands may miss something the plant needs. COBs have a blue LED that stimulates some phosphors to emit light in a broad range of different wavelengths. Apparently, the result is you don’t miss those critical absorption peaks.