Is it perhaps possible that Wyndle is a spren of Cultivation, not Honor? We know that normal spren are considered 'of Honor' while corrupted spren are considered 'of Odium'. Could it be that there are also spren 'of Cultivation', and Wyndle is one of them? Bonding a spren that is not of Honor doesn't mean someone can't be a Knight Radiant -- Renarin, after all, bonded a corrupted spren. And Wyndle is always talking about how he was a gardener, 'cultivating' things, and he also says that the other spren don't like them very much (maybe because they're different?).
It seems logical that someone who bonded an Honor-spren gets their Stormlight from actual Stormlight, because it comes from the Stormfather, who is a spren of Honor. However, getting your Stormlight from food seems to perfectly fit in with Cultivation. It's clear that Lift is in some way linked to Cultivation -- maybe just through of her boon from the Nightwatcher, but I think it's more than that, it seems like Lift was in some way 'chosen' by Cultivation. When she appears in the vision, the Stormfather is really angry, saying something like, She's doing this to annoy me. 'She' could refer to Cultivation.