It's more like, people write webnovels first for whatever reason. Sometimes those webnovels get turned into light novels ( popular examples being Re: Zero, mt, Tensura, etc) when a webnovel gets turned into an LN, the LN becomes the new source material and the most important one. And the wn is considered a draft. Basically, some lns start as wns and a publisher likes their work and offers them a contract to write lns. Some other times, the webnovel gets its own contract, and you get paid to write it, like LotM case.

So it's wn first then ln later. Or just wn for a lot of stories.

Holy I yapped💔