This is long-term planning (6+ months out). The current state of your weapon grid for each element is irrelevant. What's important is using your Miracle Tickets in a way you won't regret once the novelty of a new character wears off.

In general, I view Sol as a character you start with rather than use a Miracle Ticket on. She adds flexibility to a starter team to branch into other elements later on, based on which SSR kamihime the Gatcha gives. By the time you use a Miracle Ticket, your element should be decided and there's usually higher priority kamihime to get. If you don't already have Sol, Light is probably a bad choice. If you don't have any SSRs (why?), then Sol is an option but it's still sort of a waste of a Miracle Ticket.