The bit about plants benefitting more from intensity is, as far as I understand it, false - plants are only sensitive to light in fairly narrow wavelengths, which is why grow lights aren't necessarily white. (Source: partner is a professional horticulturist who sourced grow lights for the botanic gardens he works at)
However, GP may be right about the conversion efficiency destroying any gains that you might get from re-emitting light in only those wavelengths. The energy conversion efficiency of even the most efficient LEDs seems to only be about 50%, with the rest emitted as heat. (Source: just a quick Google, so take with a grain of salt) And then you've got the solar panel efficiency on top of that, plus any necessary voltage conversion. Definitely quite a tough ask.
However, GP may be right about the conversion efficiency destroying any gains that you might get from re-emitting light in only those wavelengths. The energy conversion efficiency of even the most efficient LEDs seems to only be about 50%, with the rest emitted as heat. (Source: just a quick Google, so take with a grain of salt) And then you've got the solar panel efficiency on top of that, plus any necessary voltage conversion. Definitely quite a tough ask.